When in umbrella mode (or through multiple profiles), users can specify
macros for EDocs based on either the {def, ...} or the {macros, ...}
arguments.

This patch replaces the prior options merging for umbrellas to use the
rebar3 tup_umerge utils to remove identical duplicates while preserving
correct ordering, and manually merges the {macros, ...} definitions
while ke eping the correct precedence rules since these appear (given
their behaviour) to be all individually extracted and passed as `{d,
...}` to  the compiler so that epp expands them. This compiler
function freaks out on any re-defined macros and explodes.

Do note that the macros with `{def, ...}` are edoc macros and do not
suffer from that issue, safely deduplicating multiple definitions.

This adds an additional loading and merging of options for EDoc using
the values from the top-level along with those specified in the
rebar.config of an umbrella application.

The app-specific config values are prepended to the global ones; this
can likely cause some problems with manual path handling, but is
unlikely to happen in practice and the rest seems to work fine based on
order

Fixes the issue in #2114

Move path management out of rebar_utils manual code path function
handling (which we leave there for backwards compat), and centralize
them to allow easier coordination of paths between plugins and deps.

On top of path handling, do a check of loaded modules to only purge and
reload those that actually need it done in order to prevent all kinds of
weird interaction and accidental purge kills. It also allows the
possible cohabitation of both at once, with a "in case of conflict pick
X" as a policy

Changing path handling in providers also highlighted a bunch of bugs in
some tests and appears to fix some in other providers, specifically
around plugins.

This is done through 3 main change groups:

- replacing `~s` by `~ts` in format strings, so that strings that
  contain unicode are properly printed rather than crashing
- adding the `unicode` argument to all function of the `re` module to
  ensure transformations on strings containing unicode data are valid
  instead of crashing (see issue #1302)
- replacing `ec_cnv:to_binary/1` and `ec_cnv:to_list/1` with matching
  functions in `rebar_utils`.

The last point has been done, rather than modifying and updating erlware
commons, because binary and list conversions can be a contentious
subject. For example, if what is being handled is actually bytes from a
given binary stream, then forcing a byte-oriented interpretation of the
data can corrupt it. As such, it does not appear safe to modify erlware
commons' conversion functions since it may not be safe for all its
users.

Instead, rebar3 reimplements a subset of them (only converting
atoms and chardata, ignoring numbers) with the explicit purpose of
handling unicode string data.

Tests were left as unchanged as possible. This may impact the ability to
run rebar3's own suites in a unicode path, but respects a principle of
least change for such a large patch.

be a little smarter when generating edocs; loof for some
sort of doc path and then replace w/e was there with the
updated doc paths

Instead of a hard crash, display an error message indicating which app
failed.

We can't report the exact failure; only EDoc does it to stdout itself
and we can't capture it.

Pre/Post hooks are run properly despite the failure, as per escript and
compile providers.

Given the topological sort applied to top-level apps, we should be able
to carry the edoc values for paths configured when more than one app
exists.

This allows multiple disjoint app to have defined cross-linking in the
documentation.

Tests pending.

Allows `pre_hooks` and `post_hooks` to fire for the `edoc` provider.

- Crashes in providers lib when no providers in a namespace are bare
- Making sure bareness matches semantics; i.e. a bare provider is
  visible, a non-bare provider is hidden.