[Find My Mouse] Adding transparency support for spotlight (#41701)

<!-- Enter a brief description/summary of your PR here. What does it
fix/what does it change/how was it tested (even manually, if necessary)?
-->
## Summary of the Pull Request
### Feature
Separate the find my mouse's spotlight area with the backdrop, so that
we could support the frequent ask - We should leave the circle
transparent in find my mouse

### Engineering:
1. Modernize the framework - From UWP composition to WASDK composition
api

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## PR Checklist

- [x] Closes: #15512
- [ ] **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

<!-- Provide a more detailed description of the PR, other things fixed,
or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

<!-- Describe how you validated the behavior. Add automated tests
wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed
- [x] Data migration: Should nota break existing experience when upgrade
- [x] Should be able to configure the background and spotlight opacity 
- [x] Should be able to work with different settings


https://github.com/user-attachments/assets/6f311c03-fa79-41d3-94bb-589d853295f4

---------

Co-authored-by: Niels Laute <niels.laute@live.nl>

src/settings-ui/Settings.UI/ViewModels/MouseUtilsViewModel.cs

@@ -55,7 +55,6 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
             string spotlightColor = FindMyMouseSettingsConfig.Properties.SpotlightColor.Value;
             _findMyMouseSpotlightColor = !string.IsNullOrEmpty(spotlightColor) ? spotlightColor : "#FFFFFF";
 
-            _findMyMouseOverlayOpacity = FindMyMouseSettingsConfig.Properties.OverlayOpacity.Value;
             _findMyMouseSpotlightRadius = FindMyMouseSettingsConfig.Properties.SpotlightRadius.Value;
             _findMyMouseAnimationDurationMs = FindMyMouseSettingsConfig.Properties.AnimationDurationMs.Value;
             _findMyMouseSpotlightInitialZoom = FindMyMouseSettingsConfig.Properties.SpotlightInitialZoom.Value;
@@ -279,7 +278,7 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
 
             set
             {
-                value = (value != null) ? SettingsUtilities.ToRGBHex(value) : "#000000";
+                value = (value != null) ? SettingsUtilities.ToARGBHex(value) : "#FF000000";
                 if (!value.Equals(_findMyMouseBackgroundColor, StringComparison.OrdinalIgnoreCase))
                 {
                     _findMyMouseBackgroundColor = value;
@@ -298,7 +297,7 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
 
             set
             {
-                value = (value != null) ? SettingsUtilities.ToRGBHex(value) : "#FFFFFF";
+                value = (value != null) ? SettingsUtilities.ToARGBHex(value) : "#FFFFFFFF";
                 if (!value.Equals(_findMyMouseSpotlightColor, StringComparison.OrdinalIgnoreCase))
                 {
                     _findMyMouseSpotlightColor = value;
@@ -308,24 +307,6 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
             }
         }
 
-        public int FindMyMouseOverlayOpacity
-        {
-            get
-            {
-                return _findMyMouseOverlayOpacity;
-            }
-
-            set
-            {
-                if (value != _findMyMouseOverlayOpacity)
-                {
-                    _findMyMouseOverlayOpacity = value;
-                    FindMyMouseSettingsConfig.Properties.OverlayOpacity.Value = value;
-                    NotifyFindMyMousePropertyChanged();
-                }
-            }
-        }
-
         public int FindMyMouseSpotlightRadius
         {
             get
@@ -978,7 +959,6 @@ namespace Microsoft.PowerToys.Settings.UI.ViewModels
         private bool _findMyMouseDoNotActivateOnGameMode;
         private string _findMyMouseBackgroundColor;
         private string _findMyMouseSpotlightColor;
-        private int _findMyMouseOverlayOpacity;
         private int _findMyMouseSpotlightRadius;
         private int _findMyMouseAnimationDurationMs;
         private int _findMyMouseSpotlightInitialZoom;