This adds settings to each provider to allow us to control if individual
fallback items are enabled or not, regardless of the provider being
enabled.
This is relevant to _all the threads where disabling fallback commands
came up_
This just adds another section to each provider's settings page, with a
list of the fallback commands.
This also has nothing to do with the "top-level apps search", which is
not really a fallback command - it's its own thing.
Ref #38288. Doesn't close that, because this only controls
enable/disable, not ranking.
From here, we should be able to add a dedicated page in the SUI that
shows all the fallbacks across all providers. That's where we'll enable
the ordering.
**WARNING:** This PR will probably blow up all in-flight PRs
at some point in the early days of CmdPal, two of us created seperate
`Exts` and `exts` dirs. Depending on what the casing was on the branch
that you checked one of those out from, it'd get stuck like that on your
PC forever.
Windows didn't care, so we never noticed.
But GitHub does care, and now browsing the source on GitHub is basically
impossible.
Closes#38081
