fix: a few more conversions to the proper casing of windows paths

[dgozman]

VSCode expects lowercase drive letter, while Playwright expects uppercase drive letter. This includes fixes from #584 and more.

To properly test this, updated vscode mock to match vscode proper, which revealed a few failing tests:

    [default] › global-errors.spec.ts:19:5 › should report duplicate test title ────────────────────
    [default] › list-tests.spec.ts:442:5 › should forget tests after error before first test ───────
    [default] › problems.spec.ts:55:5 › should update diagnostics on file change ───────────────────
    [default] › watch.spec.ts:24:5 › should watch all tests ────────────────────────────────────────
    [default] › watch.spec.ts:147:5 › should watch test file ───────────────────────────────────────
    [default] › watch.spec.ts:198:5 › should watch tests via helper ────────────────────────────────

Watch fails because it tries to watch lowercase paths in Playwright. Errors through diagnostics fail because they update with both lowercase and uppercase paths.

References microsoft/playwright#34146.
References microsoft/playwright#33671.