Fix outstanding regression related to the testing rewrite

[eleanorjboyd]

In order to move the experiment out of experimentation and make it the default method, a few regressions need to be fixed. Although all issues related to testing will not be fixed before we move over fully, the extension should be at complete feature parity with the old code before removing it to not disrupt any users. The following list of issues is things to be fixed (will add more as they become uncovered)

• symlinks: Bug: Symlinks in Testing #22658
• enable shell: Pytest discovery fails with ENOENT #22395
• cancelation token passed correctly when debugging
• parameterized tests inside classes are nested correctly: Pytest parametrized tests in a class displayed under class node instead of test node #22870
• mocking cwd causes plugin failure: Running tests via test explorer breaks when getcwd is mocked #23101

once fixed old code can be deleted, including:
#23050