This PR converts the WSL distro generator to use the registry to lookup
WSL distros instead of trying to parse the results of `wsl.exe`.
`wsl.exe` sometimes takes a very long time to launch the WSL service,
which means that on the first launch of the Terminal, WSL distros can
sometimes be missing entirely!
## References
* Also related is #6160, but I feel that deserves a separate PR for
warning when the default profile is a dynamic profile who's source
indicated it was gone.
## PR Checklist
* [x] Closes#9905
* [x] Closes#7199
* [x] I work here
* [ ] Tests added/passed
* [ ] Requires documentation to be updated
## Detailed Description of the Pull Request / Additional comments
This is maybe a little BODGY, but hey we get tons of reports of this
root cause.
## Validation Steps Performed
Ran it locally, it did well. Ran a `wsl --shutdown`, then booted the
terminal - seemed to do well. I never was able to repro the slowness
myself, but I'd suspect this'll fix it.
f9a844dbda