CmdPal: Replace FiltersDropDown ComboBox with searchable dropdown (#45747)

## Summary of the Pull Request

Replaces the ComboBox-based filter control with a DropDownButton and
Flyout containing a searchable TextBox and ListView.

- Add type-to-search: typing while button is focused opens the flyout
and filters items by name
- Designed to match appearance of the context menu
- Add keyboard navigation: `Up`/`Down `moves selection from search box,
`Enter` confirms, `Escape` clears search text (or closes if empty), `F4`
opens the dropdown
- Add `Alt+F` shortcut on ShellPage to toggle filter focus
- Style flyout to match ContextMenu (item padding, separators, search
box appearance)
- Show "No results" empty state when search matches nothing
- After confirming selection, return focus to the main search box
- Add accessibility
- Update `FilterTemplateSelector` to support both ComboBoxItem and
ListViewItem containers
- Guard against infinite loop in navigation when only separators exist

## Pictures? Moving!



https://github.com/user-attachments/assets/60e232ae-8cee-4759-a9a7-d7edbf78719e

<img width="315" height="212" alt="image"
src="https://github.com/user-attachments/assets/b6e1a895-064c-47e1-9184-26dbb46fdf05"
/>


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## PR Checklist

- [x] Closes: #41648
<!-- - [ ] Closes: #yyy (add separate lines for additional resolved
issues) -->
- [ ] **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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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

src/modules/cmdpal/Microsoft.CmdPal.UI/Strings/en-us/Resources.resw

@@ -928,4 +928,25 @@ Right-click to remove the key combination, thereby deactivating the shortcut.</v
     <value>Unpin from dock</value>
     <comment>Command name for unpinning an item from the dock</comment>
   </data>
+  <data name="FiltersDropDown.[using:Microsoft.UI.Xaml.Automation]AutomationProperties.Name" xml:space="preserve">
+    <value>Filters</value>
+  </data>
+  <data name="FiltersDropDown.[using:Microsoft.UI.Xaml.Controls]ToolTipService.ToolTip" xml:space="preserve">
+    <value>Filters (Alt+F)</value>
+  </data>
+  <data name="FiltersDropDown_DefaultText" xml:space="preserve">
+    <value>Filters</value>
+  </data>
+  <data name="FilterSearchBox.[using:Microsoft.UI.Xaml.Automation]AutomationProperties.Name" xml:space="preserve">
+    <value>Search filters</value>
+  </data>
+  <data name="FilterSearchBox.PlaceholderText" xml:space="preserve">
+    <value>Search filters...</value>
+  </data>
+  <data name="FilterListView.[using:Microsoft.UI.Xaml.Automation]AutomationProperties.Name" xml:space="preserve">
+    <value>Filter options</value>
+  </data>
+  <data name="FiltersDropDown_NoResults.Text" xml:space="preserve">
+    <value>No results</value>
+  </data>
 </root>