Find my mouse: Fix the issue find my mouse xaml island could not be run in x64 environment (#43420)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request
This pull request introduces a configuration update to the
`src/runner/runner.vcxproj` project file. The change enables undocked,
registration-free WinRT initialization for the Windows App SDK, which
can improve compatibility and reduce dependency issues in certain
deployment scenarios.

Windows App SDK configuration:

* Enabled `WindowsAppSdkUndockedRegFreeWinRTInitialize` to allow
registration-free WinRT initialization in the project file
`runner.vcxproj`.

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## PR Checklist

- [ ] Closes: #xxx
- [ ] **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
Validate in x64 environment, and it can be run without problem, no
errors any more

src/runner/runner.vcxproj

@@ -28,6 +28,7 @@
     <PlatformToolset>v143</PlatformToolset>
     <WindowsPackageType>None</WindowsPackageType>
     <WindowsAppSDKSelfContained>true</WindowsAppSDKSelfContained>
+    <WindowsAppSdkUndockedRegFreeWinRTInitialize>true</WindowsAppSdkUndockedRegFreeWinRTInitialize>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
   <ImportGroup Label="ExtensionSettings">