fix(windows): clear diagnostics errors

[mxschmitt]

Whats happening?

The issue is that we write errors to a Map with "Node.js like paths" so that the drive-letter is uppercase but we delete them out of the map by using the VSCode workspace change event, which are VSCode like paths, which have always lowercase drive letters.

This PR wraps when calling set inside this._vscode.Uri.file(path).fsPath which normalises and is what we already do for other places when we interact with locations from the reporter API.

playwright-vscode/src/testModel.ts

Lines 395 to 396 in ffcd83a

	for (const requestedFile of requestedFiles)
	this._errorByFile.deleteAll(requestedFile);

Resolves microsoft/playwright#34146
Resolves microsoft/playwright#33671

[dgozman]

Please add a test. Overall, I don't like how we sprinkle this pattern in some places, but not consistently. We need to figure out a nice boundary where we convert between Node.js paths and VSCode paths and stick to that, hopefully enforced by TypeScript. Any ideas?