fix typo(s)

Fix various DDOC warnings

Move foreign code from global scope to dub.internal. ...

Avoids conflicting with the actual dub packages when working with dub as a library. Also, even if just by convention, it ensures that dependent code doesn't rely on this code as a public API.

Merge remote-tracking branch 'upstream/stable' into merge_stable

Fix #1752: Use 'no' as string representation of Dependency.Invalid

sumtype: Work around bugs in return type inference

Do not use Phobos' sumtype, use dyaml's versioned one ...

So that we can compile with older versions of the frontend,
currently v2.097 instead of v2.098.

Trivial: Remove redundant comparison ...

optional and default_ are indeed checked by opEquals.

Trivial: Correct code to use match's value instead of property ...

This code was accidentally working as it was calling the path property,
essentially entering another match on the SumType.

Remove 'unknown' version ...

It was never used.

Dependency: Deprecate path/repository setters ...

There is no real use case for changing a dependency in place,
instead we better let the user overwrite the dependency itself.

Trivial: Expand body of Dependency.opEquals ...

While the m_value difference is the common case,
the other ones need to be checked as well,
so put them first as they are cheaper.
Additionally, having three expressions on a single
return is not ideal for coverage / break,
so split it into 3 lines.

Dependency: Make VersionRange.match scope

Dependency: Take advantage of -preview=in ...

Since -preview=in is now used by dub for Configy,
we might as well take advantage of it here too.

improve some output coloring ...

See #2347

Deprecate Dependency.versionSpec ...

All places which assumed that Dependency contained a VersionRange have been culled,
so we can now start removing those properties.

Trivial: Move relevant documentation from Dependency.versionSpec to VersionRange

Dependency: Expose `visit` to `match` on `SumType` ...

To do so, we need to expose `VersionRange`.
The function is a free function as it otherwise triggers
a deprecation for dual contexts due to the template parameters.

Add some const qualifiers to Repository

Trivial: Sort inner type in Dependency consistently

Dependency: Ensures call to version_ are on version-containing object ...

The initial port of Dependency to SumType kept full backward compatibility
for ease of use and review, but we can start now to weed out bad usages, if any.

Deprecate Dependency.matchesAny in favor of VersionRange

Keep logging functionality out of the public API as requested in https://github.com/dlang/dub/pull/2124#issuecomment-813016939.

New logging module - initial functionality ...

The new module replaces dub.internal.vibecompat.core.log by using the
same function names, but implementing colored output and the left
fixed-width tag. Overloaded functions are provided to output colored
text.

Still missing initLogging() and non-TTY stdout/stderr detection

Dependency: Remove dead 'isSCM' code from Version ...

Before `Dependency` was made to use `std.sumtype`,
the code was piggybacking on a field `VersionRange m_range` to store
the git reference whenver the `Dependency` was a `Repository`.
Since this is no longer the case, we can remove this exception from `Version`.

Dependency: Convert to a discrete type ...

A major issue when dealing with the 'Dependency' type is that it evolved from a simple type,
which stored a version range and perhaps one or two boolean,
to one that stores 4 kinds of dependencies: version range (including exact version),
branches, repository + hash, and path.
Instead of using a discrete type (e.g. a tagged union), the type is a mix of style,
and repository and branch are piggybacking on the field used for the version range.

Switching to std.sumtype makes interaction between fields more obvious.
Most importantly, it forces the programmer to answer the hard questions,
such as how do we compare completely different dependency (version vs repository).

Hopefully this will make the code easier to understand, and in the future,
make it easier to add a new kind of dependency.

Add VersionMatchMode support to VersionRange.matches

Suppress `version` for path-based deps in Dependency.toJson() ...

As in dub v1.29 and before.

Dependency: Remove top-level safe, apply to decl ...

A top level safe means that we cannot have templates in this structure
that infer their safety, which can be severely limiting.

Dependency: Change format for path-based dependencies (#2316) ...

* Add missing attributes to NativePath.empty

* Dependency: Change format for path-based dependencies