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

Move `absolute_path/2` and `normalized_path` to `rebar_file_utils`

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`).

rebar_git_resource: fix {vsn, git} parser

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

rebar3: ipv6 support for proxy

Switch to EPP analysis covering all apps at once when compiling

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

Fix race condition in rebar_prv_shell boot

rebar_compiler_dag: implement single-pass pruning

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.

OTP-23 compatibility and warning removal

Allow specifying the outdir in bare compiler

- 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 08eb611a3d)

(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)

force use of tls1.2 for http fetching to work on OTP-23-rc1

re-enable use of rebar_packages_cdn in rebar_pkg_resource

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

This commit is a transition point that makes some assumptions about new
callbacks for the compiler modules, which will likely not hold when it
comes to making epp be able to read and handle multiple applications at
once (so it can resolve parse transforms and behaviours across OTP
apps).

As such, a follow-up commit is going to be completing that one and
changing its API in incompatible ways; if you find this commit during a
bisect, it's probably not a good one in which to run a bisection.

Source file encoding specifier support for template

This reverts commit 025a96b143.

only write lock file if locks have changed

Solves #2071, IPV6 support for proxy, by trying to resolve proxy
host name without specific IP address family. If it fails, it
attempts a different IP family, and in case that succeeds, it
sets up HTTP client profile to use IP family that worked.

rebar_git_resource: allow non-single-digit git versions

rebar_dir: return _checkouts path in a canonical form

This enables relative paths for checkouts_dir configuration variable.

It is quite normal to have git 2.17.1 on MacOS X.

Bump cth_readable (1.4.8) to fix assertion macros

Fix bootstrap crashes when compilers get modified

When recompiling rebar3 itself, the path swaps and cleaning removes the
modules loaded from _build/bootstrap, but the VM still manages to
discover those in _build/prod from previous builds of the escript when
building the new escript, which causes weird failures when compilers get
modified between releases.

The fix is to just clear _build/prod as part of the init of the
bootstrap script, the same way we already clear _build/bootstrap.

Eliminate lock file warnings when upgrading from 1.1.0 locks

The code was written at the time only one lockfile version was being
explicitly tagged (1.1.0), and all the other older ones were untagged.
In introducing the 1.2.0 format for external hashes, the current version
check still took place, but no provisions were made to explicitly check
between older or newer versions. As such, rebar3 would warn (prompting
people to upgrade) every time a lockfile on the 1.1.0 version (which is
likely over 99% of those in the wild as of today) would be encountered,
we'd prompt people to upgrade.

This patch introduces a constant for the list of supported tagged
versions for config/lock files, which allows to drop warnings when
rebar3 can transparently upgrade the lock file for the user.

It pre-supposes a potential "unsupported lock file" error could be added
in the future if a config format is not newer but in fact explicitly
deprecated. This isn't implemented but the current logic works towards
making that support possible.