Tests: Fix vfs paths on Windows ...

With our versioned path implementation, we have the following issue:

assert(NativePath("/foo").absolute); // Passes
assert(NativePath(NativePath("/foo").toNativeString()).absolute); // Fails

However, instead of fixing the implementation, we provide
a different root for the VFS, which is arguably simpler but
also more correct.

Hoist imports and remove versioning in FilesystemPackageSupplier ...

Hoisting imports to have them all in the same place.
Also remove a version statement, as the client code should not
care if vibe-d is being used and just import the internal module.

Clear up unprinted deprecation for overrides ...

This code should have triggered a deprecation, however it didn't
get printed for some unknown reason. Turning on '-de' leads to seeing
it. The fix is fairly straightforward and doesn't affect the code.

Use the proper constructor for PackageDependency ...

This code was using a deprecated constructor, but as it was in lambda,
it didn't trigger a deprecation message, however '-de' points us to
the issue.

Tests: Fix writeFile implementation with vibe-d ...

This was triggering an assert error with vibe-d path.
The recursion logic was a bit murky, so the function
is now split in 3 different part and better documented.

Make all overloads of download private ...

Since this is not used directly anywhere inside of dub,
make it private so it can be later refactored.

Upgrade checkout and codecov to latest version ...

Get rid of a deprecation message about Node 16.

Tests: Simplify loadSCMPackage implementation ...

Now that we can override the git clone operation and load
from the virtual filesystem, we can remove a lot of the
duplicated logic. This is currently hardcoded to a dub.json,
but future iterations can store an FSEntry representing the
full package.

Tests: Add the ability for TestDub to use an initialized filesystem ...

This way, we can test any kind of crazy conditions found in bug reports,
such as the behavior in the face of non-writeable filesystem.

PackageManager: Move addPackages inside loadGitPackage ...

This avoids calling addPackages when the package is already loaded,
and will allow us to handle PlacementLocation correctly in the future.

Allow better dependency injection on PackageManager's SCM operation ...

What we really want to override is the git clone operation,
so one way to approach this is to decouple it from the rest
of the code, then when our virtual filesystem is complete,
we will only need to override that one function.

Tests: Move root FSEntry from PackageManager to TestDub ...

This way we can extend its use to all of TestDub.

Trivial: Make TestDub.ProjectPath a NativePath ...

If unittest code wants to reference it, it will be much more useful as NativePath.

Fix #2840: Build collision for single-package and FILE_FULL_PATH ...

By including the package path in the buildid we avoid the problem,
at the expense of not sharing the cache for packages that could be
shared, but we would need to know if the code depends on __FILE__
and __FILE_FULL_PATH__ or not.

CI: Run all tests when coverage is enabled ...

A recent change in the CI enabled coverage, however it did so on
the latest tags, meaning we were no longer running the other
tests (from the testsuite). This corrects it.

CLI: Slightly reduce memory allocations ...

By improving commandNames to only allocate once (the array call) instead
of many times (once per CommandGroup + join call),
as well as removing a call to commandNames and using a simple getter.

CLI: Simplify extractCommandNameArgument

Make 'Dependency.init' invalid and align Any/Invalid property ...

VersionRange has Invalid and Any while Dependency has invalid and any.
One has to go, and it's going to be Dependency's.
In addition, make sure that the 'init' state of Dependency is a known state.

Add a CI step to upload assets on release creation ...

We haven't had assets generated for releases since v1.29.0,
however some external code depend on them (dlang-community/setup-dlang, namely).
This will fix it and make it less likely to be forgotten in the future.

Adapt DependencyResolver to PackageName API

Add opEquals/opCmp to PackageName

Update configy to the latest HEAD

Merge pull request #2835 from ibuclaw/merge_stable ...

update version to v1.36.0

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

update version to v1.36.0

Trivial: Slightly simplify PackageManager.store

Merge pull request #2833 from ibuclaw/merge_stable ...

merge stable

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

update version to v1.36.0-rc.1

Build the tests and binary with -cov on POSIX ...

The CI was sending empty coverage reports because nothing
was being generated, as the variable was always false.
In the process, a bit of dead code was removed.