Add unittest to test collection of C sources and headers

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

fix #2587

fix typo(s)

Reduce dependency on `std.file` (#2547)

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.

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: Fix typo in documentation

Use configy library to parse dub.json file ...

This will provide a vastly superior UX to the users:
- They will be warned about typos;
- The type information provided will be more accurate and always include file/line infos
  (e.g. no more 'Invalid SemVer versions');
- We can expose a better recipe struct to library users on the long run,
  by separating the actual data DUB uses from what it reads;
- We can be more descriptive about errors / intent, for example by using `SetInfo`;

Integrate `dependencyBuildSettings` into dependencies ...

Because those are specified in `dependencies`,
they should be stored alongside them.
Unfortunately this will slihtly increase memory usage in the common case,
but unlikely to a point where it would be problematic.

This is technically a breaking change as a field is getting removed,
however this struct has been manipulated a few times in breaking ways,
and it's unlikely `dependencyBuildSettings` is being used outside of dub,
given how recent it is and how narrow its usage is.
However, as `dependencies` is likely to be widely used, a compatibility
type and an `alias this` are provided not to break client code.

Trivial: Add attributes and documentation to PackageRecipe ...

While the attributes aren't used yet, they are self-descriptive,
and they improve code readability.

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

Add SumType support to packagerecipe : clone ...

clone does not support enum, but it can support discriminated enums.

Remove leading hyphen in platform specs ...

It doesn't serve any purpose.

[add BuildSettingsTemplate.dup() method instead]

Build{Options,Requirements}: Use a common templated struct ...

A bit less copy-pasta is a small but appreciable win.

Fix injectSourceFiles not going into description or actually working

Implement injection of source files from dependencies into parent final binaries (executed/shared libraries)

Add environment variables to BuildSettings (#2121)

Refactor import. inet.path is publicly imported from inet.url, but only symbols from inet.path are used.

Add dependencyBuildSettings to BuildSettingsTemplate

Replace occurences of 'in ref' with 'const scope ref' ...

In support for dlang/dmd#11000

Allow hidden paths that are specifically referenced from the dub recipe ...

file. Finish out the test case for ignoring unreferenced hidden paths
and making sure referenced ones are compiled.

fix #1372 - Ignore files in hidden directories.

Cache environment variables in collectFiles for a small speed boost (~10ms)

Perform the tool chain checks based on the compiler name. ...

Gets rid of the additional methods in the Compiler interface and moves the checks to a more central location, since other generators apart from BuildGenerator might want to perform the checks in the future. Also keeps the API "package" for now to avoid adding insufficiently though-out public APIs.

Change toolchainRequirements fields to Dependency. ...

Also removes some API clutter from Compiler and PackageRecipe.

Merge pull request #1571 from rtbo/requirements ...

toolchainRequirements recipe support
merged-on-behalf-of: Nicholas Wilson <thewilsonator@users.noreply.github.com>

toolchainRequirements recipe support