Description of the new feature/enhancement

It'd be nice if the "Windows PowerShell" profile worked like the other profiles, and could be disabled using disabledProfileSources.

This would remove the need to carry a 'hidden' overriding profile per #5459, as disabledProfileSources made possible for the other profile sources.

Proposed technical implementation details (optional)

I guess it just needs new IDynamicProfileGenerator implementation, that replaces (and slurps up?) the existing Windows PowerShell profile if present, which appears to have a fixed GUID ({61c54bbd-c2c6-5271-96e7-009a87ff44bf}), fix the 'pick a default profile' logic, and then remove it from the defaults.json.

If the same thing is done for CMD, then I guess the risk appears of how to handle the case that there are no profiles available, where right now I guess you always have those two profiles, even if somehow they are not usable.