Python interpreters on Windows are reported as 'Unknown'

[kimadeline]

On master, commit 1768483, after having added the readdir fix for #10850 manually:

Interpreters installed from the Windows Store are of type Unknown because they are found through the KnownPathService locator, and not WindowsRegistryService:

And interpreters installed from python.org are also of type Unknown because they are found using the WindowsRegistryService locator:

[karthiknadig]

The spike is to find more places where we use UNKNOWN

[karrtikr]

No longer valid.