Fix issue 2258 and copy the build artifacts to the target directory

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

Fix #2238 - Renew source files after preGenerateCommands

Define the $DUB_BUILD_PATH variable. ...

The `$DUB_BUILD_PATH` variable is now defined inside the `postBuildCommands`
section. It contains the absolute path in which the package was built, and can
be used to copy by-products of the build process to their intended locations.

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

Windows: Copy .pdb files ...

Fixes #1962.

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

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

Generate paths relative to visuald project files (#2150) ...

Fixes #1477 : Internal paths for sources etc in projects should be relative to project file path. Actually relative to "working dir"/.dub

Don't reduce the max path length on Windows even further ...

Fixes #2143.

Add environment variables to BuildSettings (#2121)

Add lowmem for settings

Fix single file package dynamic library

Actually copy copyFiles when building in Visual Studio. (#2105) ...

Actually copy copyFiles when building in Visual Studio.
merged-on-behalf-of: Max Haughton <maxhaton@users.noreply.github.com>

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.

Merge pull request #2098 from veelo/issue2085 ...

Fix #2085: [visuald] spurious library project
merged-on-behalf-of: Petar Kirov <PetarKirov@users.noreply.github.com>

If no output is generated (TargetType.none) then don't generate a project configuration. ...

This prevents VS from attempting to build a library with no name from no sources.
Fixes #2085.

Remove unused imports.

Selectively import symbols from std.array.

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

Set cwd on spawn functions instead of chdir ...

It is more hygienic to use the cwd argument as it doesn't impact
the running process, and doesn't decouple the reason for it.

Remove redundant code with relativeTo ...

The versioned code was doing almost the same thing as relativeTo,
but adding `./` or equivalent so it could be run from the cwd.
Instead of doing this complicated patching, just use the absolute
path for running, but the relative path when issuing messages to the user.

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

Merge pull request #2040 from omerfirmak/agora-1327 ...

Allow custom dflags to be defined for dependencies

Don't export DFLAGS & LFLAGS to nested invocations by default

Recursively apply dependencyBuildSettings ...

For now, only "dflags" is used

Use compiler version, not frontend version for build IDs and paths ...

This prevents artifacts from being reused after upgrading the compiler
from a beta to a final or to a newer patch release.