Add unittest to test collection of C sources and headers

Make getDUBExePath returns a NativePath

fix typo(s)

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

reduce dependency on the working directory ...

Improves library API usage and bugs with the build generator

Remove GeneratorSettings.direct as it is never set

Use a central build cache for all build artifacts ...

Currently the central build cache is not configurable,
but as most build artifacts end up in `~/.dub/packages/` anyway,
this will be a positive change for users.

Replace all instances of mkdirRecurse with ensureDir ...

All usages actually want to ensure the directory is present,
and don't care about having a separation between existence check
and creation.

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.

Recursively link all link deps of dynamic libraries too (#2414) ...

Templates exposed by a dynamic library A can easily lead to
instantiations in dependees needing to be linked against a direct or
indirect dependency of A.

Minor: Replace a foreach with a nested function ...

Avoid an allocation every time and a cast.

improve some output coloring ...

See #2347

Address review by WebFreak001.

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

More improvements and replacements ...

Adapted generators output to new style, small change for non-selected
packages

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

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

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

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

Fix #2238 - Renew source files after preGenerateCommands

move command variable substitution to execution ...

This is needed as commands that need to be run need to have generator
settings available before running to avoid inconsistencies with
environment variables passed to the actually ran program and variables
used in substitution.

Fixes #2192

Fixes pre/postGenerateCommands inconsistently using dub environments
(execution was substituted including buildEnvironments, but shell cmd
did not get the build variables for substitution) - now both get
the build variables. Solved by removing code duplication. (env building)

This commit changes the behavior of `dub describe` so that describing
commands settings no longer substitutes variables. Before, known
variables would have been replaced in the output and on unknown
variables `dub describe` would fail with an error
`Target 'x' doesn't exist`

Now exposes some previously private project.d processVars functions

Removes dynamicLibrary being built as staticLibrary for targets other than OMF

Fix build setting inheritance ...

First inherit upward then force the dependency build settings
downwards. Fixes the dependency build settings leaking upwards.

Fixes #2176
Fixes #2177

Add environment variables to BuildSettings (#2121)

Add lowmem for settings

Fix single file package dynamic library

Merge pull request #2099 from veelo/issue1053-visuald-extra-files ...

Include copyFiles and extraDependencyFiles in visuald projects.

Merge pull request #2087 from veelo/issue2086-copyFiles-subPackage-targetPath ...

Fix #2086 copyFiles in subPackage does not honour targetPath.

Include copyFiles and extraDependencyFiles in visuald projects. Resolves #1053.

Selectively import symbols from std.array.

Fix issue #2086: Copy files of sub packages to the target path.