This doesn't actually have a UX to expose this yet - we need to stack a
couple of PRs up to get to that.
But this adds plumbing such that we can now stash away a command ID, and
retrieve it later as a top-level command. Kinda like pinning for apps,
but for _anything_.
It works off of a new command provider interface `ICommandProvider4`,
which lets us look up Command**Item**s by ID. If we see a command ID
stored in that command provider's settings, we will try to look it up,
and then load it from the command provider.
e.g.
```json
"com.microsoft.cmdpal.builtin.system": {
"IsEnabled": true,
"FallbackCommands": {
"com.microsoft.cmdpal.builtin.system.fallback": {
"IsEnabled": true,
"IncludeInGlobalResults": true
}
},
"PinnedCommandIds": [
"com.microsoft.cmdpal.builtin.system.lock",
"com.microsoft.cmdpal.builtin.system.restart_shell"
]
},
```
will get us
<img width="840" height="197" alt="image"
src="https://github.com/user-attachments/assets/9ed19003-8361-4318-8dc9-055414456a51"
/>
Then it's just a matter of plumbing the command provider ID through the
layers, so that the command item knows who it is from. We'll need that
later for actually wiring this to the command's context menu.
related to #45191
related to #45201
_targets #40504_
Major refactoring for #40113
This moves a large swath of the codebase to a `.Core` project. "Core"
doesn't have any explicit dependencies on "extensions", settings or the
current `MainListPage`. It's just a filterable list of stuff. This
should let us make this component a bit more reusable.
This is half of a PR. As I did this, I noticed a particular bit of code
for TopLevelVViewModels and CommandPaletteHost that was _very rough_.
Solving it in this PR would make "move everything to a new project" much
harder to review. So I'm submitting two PRs simultaneously, so we can
see the changes separately, then merge together.
