Merge both TestDub constructors ...

Those constructors had different but non-overlapping functionalities.
In the event one wanted to set one of the parameters passed to Dub
constructor but also initialize the FS, one was out of luck.

Remove FileInfo.timeCreated ...

As it is not available on all platforms, we can't really rely
on it for code, and it is indeed not used anywhere.

Tests: FSEntry.writeFile write to wrong directory ...

This was a subtle bug hidden by the fact that 'parent' exists
in the class. It was causing problems when calling 'print',
but luckily didn't affect anything else.

Test registry: Store version separate from Package ...

This will allow us to store full packages (FSEntry) instead of
the processed / already instantiated Package.

Introduce readText and make stripUTF8BOM private

Load dub.selections.json in unittest ...

Allow better testing by loading already resolved dependencies.

Merge pull request #2866 from Geod24/mlang/Simplify1 ...

Trivial: Simplify PackageManager's loadInternal

Move writing selections file to PackageManager ...

The PackageManager is the main source of IO in Dub,
and having it take responsibility for writing the
selections file reduces the number of special casing
we need to make when doing dependency injection.

Merge pull request #2865 from dlang/fix_issue_2691_reboot ...

Properly fix issue #2691 by reverting to the original scanning behavior

Simplify condition.

Trivial: Simplify PackageManager's loadInternal

Properly fix issue #2691 by reverting to the original scanning behavior. ...

Reverts to the scanning/warning behavior that was in place before the warnings for the new package directory structure were implemented.

Revert "Fix #2691: Use same structure for managed and unmanaged path" ...

This reverts commit 1a53049.

Remove an unused JSON serialization call ...

This was completely unused in the function.

Tests: Use TestDub FSEntry constructor for more accurate tests ...

The previous approach added Packages in the PackageManager directly,
completely sidestepping the scanning the PackageManager does,
which is a behavior we absolutely want to test.

By setting up the filesystem before we instantiate our `TestDub` instance,
we can remove a bunch of exceptions / overrides, and get a much closer
behavior to the final product.

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.