CmdPal: Icon cache (#44538)

## Summary of the Pull Request

This PR implements actual cache in IconCacheService and adds some fixes
on top for free.

The good
- `IconCacheService` now caches decoded icons
- Ensures that UI thread is not starved by loading icons by limiting
number of threads that can load icons at any given time
- `IconCacheService` decodes bitmaps directly to the required size to
reduce memory usage
- `IconBox` now reacts to theme, DPI scale, and size changes immediately
- Introduced `AdaptiveCache` with time-based decay to improve icon reuse
- Updated `IconCacheProvider` and `IconCacheService` to handle multiple
icon sizes and scale-aware caching
- Added priority-based decoding in `IconCacheService` for more
responsive loading
- Extended `IconPathConverter` to support target icon sizes
- Switched hero images in `ShellPage` to use the jumbo icon cache
- Made `MainWindow` title bar logic resilient to a null `XamlRoot`
- Fixed Tag icon positioning
- Removes custom `TypedEventHandlerExtensions` in favor of
`CommunityToolkit.WinUI.Deferred`.

The bad
- Since IconData lacks a unique identity, when it includes a stream, it
relies on simple reference equality, acknowledging that it might not be
stable. We might cache some obsolete garbage because of this, but it is
fast and better than nothing at all. Yet another task for the future me.

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## PR Checklist

- [ ] Closes: 
- [ ] Closes: #38284
- [ ] Related to: #44407
- [ ] Related to: https://github.com/zadjii-msft/PowerToys/issues/333
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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## Detailed Description of the Pull Request / Additional comments

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## Validation Steps Performed

.github/actions/spell-check/expect.txt

@@ -899,6 +899,7 @@ LEFTTEXT
 LError
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 LExit
+LFU
 lhwnd
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