Move virtual environment test context into main context (#4370)

It was becoming problematic that the virtual environment test context
diverged from the other one i.e. we had to implement filtering twice.
This combines the contexts and tweaks the `TestContext` API and
filtering mechanisms for Python versions. Combined with my previous
changes to the test context at #4364 and
#4368 this finally unblocks the
snapshots for test cases in #4360 and
#4362.

.github/workflows/ci.yml

@@ -168,7 +168,7 @@ jobs:
     steps:
       - name: Create Dev Drive using ReFS
         run: |
-          $Volume = New-VHD -Path C:/uv_dev_drive.vhdx -SizeBytes 10GB |
+          $Volume = New-VHD -Path C:/uv_dev_drive.vhdx -SizeBytes 12GB |
                     Mount-VHD -Passthru |
                     Initialize-Disk -Passthru |
                     New-Partition -AssignDriveLetter -UseMaximumSize |