Find My Mouse: Handle default color for brand new settings (#42182)

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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
Give a default color transparency as before instead of leave background
black and foreground white.

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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
1. Delete setting for find my mouse
2. Start find my mouse, the backdrop and foreground are semi-transparent
3. Start settings, and the default settings should persist correctly.
4. Start powertoys again, make sure the default color is still
semi-transparent
5. Other settings change can be handled and persisted correctly

---------

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

src/modules/MouseUtils/FindMyMouse/FindMyMouse.h

@@ -12,8 +12,8 @@ enum struct FindMyMouseActivationMethod : int
 
 constexpr bool FIND_MY_MOUSE_DEFAULT_DO_NOT_ACTIVATE_ON_GAME_MODE = true;
 // Default colors now include full alpha. Opacity is encoded directly in color alpha (legacy overlay_opacity migrated into A channel)
-const winrt::Windows::UI::Color FIND_MY_MOUSE_DEFAULT_BACKGROUND_COLOR = winrt::Windows::UI::ColorHelper::FromArgb(255, 0, 0, 0);
-const winrt::Windows::UI::Color FIND_MY_MOUSE_DEFAULT_SPOTLIGHT_COLOR = winrt::Windows::UI::ColorHelper::FromArgb(255, 255, 255, 255);
+const winrt::Windows::UI::Color FIND_MY_MOUSE_DEFAULT_BACKGROUND_COLOR = winrt::Windows::UI::ColorHelper::FromArgb(128, 0, 0, 0);
+const winrt::Windows::UI::Color FIND_MY_MOUSE_DEFAULT_SPOTLIGHT_COLOR = winrt::Windows::UI::ColorHelper::FromArgb(128, 255, 255, 255);
 constexpr int FIND_MY_MOUSE_DEFAULT_SPOTLIGHT_RADIUS = 100;
 constexpr int FIND_MY_MOUSE_DEFAULT_ANIMATION_DURATION_MS = 500;
 constexpr int FIND_MY_MOUSE_DEFAULT_SPOTLIGHT_INITIAL_ZOOM = 9;
@@ -43,4 +43,4 @@ int FindMyMouseMain(HINSTANCE hinst, const FindMyMouseSettings& settings);
 void FindMyMouseDisable();
 bool FindMyMouseIsEnabled();
 void FindMyMouseApplySettings(const FindMyMouseSettings& settings);
-HWND GetSonarHwnd() noexcept;
+HWND GetSonarHwnd() noexcept;