handle windows paths beginning with \\?\

[connorskees]

This should resolve #94961. It does so by optionally allowing drives to be prefixed by \\?\.

@Tyriar

[msftclas]

All CLA requirements met.

[connorskees]

I'm having trouble replicating the CI errors locally. yarn run mocha --run src/vs/platform/backup/test/electron-main/backupMainService.test.ts says everything is fine, but in CI it timed out,

1) BackupMainService dedupeFolderWorkspaces should ignore duplicates on Windows and Mac (root workspace):
Error: timeout of 5000ms exceeded. Ensure the done() callback is being called in this test.

Should I just retry it?

[Tyriar]

Seems like a flake, also the ci.yml one can probably be ignored so this looks all good. Thanks for covering the new developments too with terminalValidatedLocalLinkProvider.test.ts 😄