Into a standalone module where it can be reused for optimisation work
later on.

Cleans up some annoying broken abstraction.

Also fix erl_first_file artifact tracking, which will avoid seeking to
disk by finding the opts in the DAG

This reverts commit f0c8c202af.

Because the resource doesn't absolutely require using a sparse
checkout, it only matters that rebar3 knows the correct path of the
application, the resource is named git_subdir.

It has to be git specific because the reason this subdir support is
special is the need to keep the code checkout as a usable git clone
to run commands against. This means the resource can't just copy
the content of the subdirectory to the application out directory.

End result should allow to look like this:

    $ head -n 3 rebar3
    #!/usr/bin/env escript
    %% Rebar3 3.14.0-rc1
    %%! +sbtu +A1

This will allow tools like mix to read the top of the file to know the
version being used in the current path (when using features that aren't
forwards-compatible) without having to invoke the tool itself.

The version (full dynamic one) is also added to the local install:

    $ head -n 2 /home/ferd/.cache/rebar3/bin/rebar3
    #!/usr/bin/env sh
    ## Rebar3 3.14.0-rc1+build.4599.ref6b0f90d

The `##` comments are used to keep a fixed width over the other form.

To be backported to 3.13.2 as well.

This commit switches the relx dependency to branch 4.0.0. It is the
first iteration of integration with relx 4.0 which adds many changes
to how relx works and how the two integrate.

rebar_relx module now creates a relx state from the relx configuration
and pass it along with all the OTP applications rebar3 knows about
which may be used in the release. This allows relx to not have
to duplicate the effort of application discovery like before.

Since this is intended to be released only when OTP-23 is released
the testing of OTP-18 has been removed.

- topsort of an app does a full analysis of all apps to come up with
  their app-level DAG
- each extra_src_dir has its own analysis run
- each extra_src_dir run is simulated as being an app
- we therefore end up doing a lot of useless analysis for single app
  runs

This patch notes runs with 1 or 0 apps and skips doing the topsort
analysis on them, which speeds things up further.

Would close erlang#2202. In case of no apps found when calling
`rebar_state:project_apps(State)` rebar3 now throws an error with
a warning.

Closes #2108. Changes the path to be printed to a relative path
to the current directory.

Also removes the `exports_not_used` warning from the default ones,
as Tristan suggested.

Also fixes artifacts left on filesystem, and produces less
filelib:last_modified() checks.

now all sources have at least one edge with 'artifact' label,
let's ignore it when choosing whether to compile in parallel
or sequentially

The propagation was confusing source files and artifacts; the artifact
ordering was flipped, and the tagging non-mandatory (aside from as
edges), which made things hard to identify when plugins for compilers
are used.

Now it should work in Erlang/OTP versions earlier than 20 and
update the symlink in case of one already existing (so that `last`
always points to the last run).

This patch enables two features:
 * in rebar.config, {diazlyer, [{plt_apps, all_apps}]} makes rebar3 to
   add all project files into PLT for subsequent analysis
 * rebar3 ct --app=myapp allows single application success typing

This allows workflow suitable for large codebases:
 * "rebar3 ct dialyzer --succ-typings=false" to build PLT with all apps
 * "rebar3 ct dialyzer --app=myapp" to perform success typing of myapp

Implements #1734. In case of not being able to create the
symlink rebar3 warns through `?DEBUG`.

As suggested in #2223, `make_absolute_path/2` and `make_normalized_path/2`
should, instead of being exported in `rebar_dir`, be moved to
`rebar_file_utils` and renamed (decided to simply remove the `make`
from their names since in that module there is already a path related
function called `canonical_path`).

This allows to do quicker re-compile option validation by not requiring
to access the disk and check all candidate erlang files for option
changes. This also opens up the way to compilers that produce more than
one artifact per file.

rebar3 uses following git invocation when it needs to generate
vsn to put into app.src:
git -c color.ui=false log --oneline --no-walk --tags --decorate
It may return something like some_repo/some_project/12345678,
with some characters preceding actual hash. This leads to some
unusual version written into application resource file, e.g.
{vsn, "some_repo/some_project/123456678"}.
This does not work well with semantic versioning, and also
produces unexpected OTP application names and folder names,
e.g.
myapp-some_repo/some_project/12345678

THat was code written on a bus and rarely executed, but still the
function called didn't exist for real.

Reduces dependency verification time for large codebases.

Fixes https://github.com/erlang/rebar3/issues/2242
Filters out dead processes that can't return process info.

- Normalize path behaviour to always be "/" across versions
- Normalize port visibility behaviour to match input string when
  appending
- restore rebar_utils function to avoid breaking random plugins that
  peek into our libs for their stuff
- Support URIOpts equivalent and protocol-based overrides; the behaviour
  there is not necessarily consistent across versions in terms of what
  ports are returned (http_uri always returned a port but uri_string
  only returns it if explicitly specified -- we choose the latter
  behaviour on newer releases), but the calls work to ensure URI parsing
  consistently works across versions

The latter judgement call is a bit of an odd one; for consistency we
could always mandate ports, but this would come at a performance penalty
when appending URL paths (i.e. when fetching packages).

The reason for this is that we standardize on the new uri_string
behaviour for path appending (if the port wasn't specified, we don't add
it), and with the http_uri rules, we need to do a kind of parsing round
that checks if the port was included or not to make it equivalent. This
is costly, and _not_ returning the port when it isn't specified lets us
do this transparently.

This allows to maintain backwards compat in older append functions, and
nobody aside from us currently uses the new rebar_uri module so we can
decide to introduce this potential inconsistency if we wish to.

(cherry picked from commit fa577bc46e)

Attempts to bridge http_uri (deprecated in OTP 23)
and uri_string (available as of OTP 21+).

(cherry picked from commit 7057cbe281)

Currently, we just write to ebin/ in the current working directory; this
implies that the source _should_ always be in the same subpath as the
ebin/ directory.

In the cases of utils like Mix, which store downloaded dependencies in
deps/ and artifacts in _build/, this may force more rebuild or less
caching that would be ideal.

This PR adds --outdir / -o as options to the bare compiler, which lets
the user specify another path, with a default kept to $CWD.

- Can't deal with := in map type declarations
- maps:update_with didn't exist back then so we reinvent it for the few
  months until we deprecate OTP 18

This moves the old DAG stuff out from the main code paths and
substitutes it with the new epp-based DAG work.

Also fixes previous work for integration tests:

- consider ptrans from erl_opts in app ordering
- display proper app compilation info messages due to reordering

While leaving the old one in place, prep the ground for new analysis
phases for the DAG work. The new DAG functions are added, but not hooked
in yet.

Fixes to the EPP handling have also been added due to issues in
resolving include_lib information