[Keyboard Manager] Toggle module hotkey/shortcut (#42472)

## Summary of the Pull Request

Adds a keyboard shortcut to be able to toggle the Keyboard Manager
module on and off.

## PR Checklist

- [x] Closes: #4879 
- [x] **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

## Detailed Description of the Pull Request / Additional comments

Modeled the changes and addition of a global shortcut using the Color
Picker module.

Notes:
- This uses `KeyboardManagerSettings` and the associated .json settings
file. I don't think there's anything else in this module that uses this.
- The default key binding for this is `winkey + shift + k`
- I've had to update the `KeyboardManagerViewModel` to extend
`PageViewModelBase` as opposed to `Observable` to get it to work. But I
will say that there were some things in here that I didn't fully dig
into, so let me know if there's any potential things I'm missing.
- I'm not too sure how to update the Settings UI after a hotkey is
pressed (pressing the hotkey currently will not show the module being
toggled off) - can't find a good way to refresh the settings ui after
enabling/disabling the module. Any pointers here would be appreciated!



## Validation Steps Performed
- Manually validated the following items:
  - Using the default shortcut (`winkey + shift + k`)
  - Changing the shortcut
  - Ensuring the change is persistent

## Media


https://github.com/user-attachments/assets/e471b8df-787a-441e-b9e0-330361865c76

---------

Co-authored-by: Weike Qu <weikequ@get-stride.com>
Co-authored-by: Leilei Zhang <leilzh@microsoft.com>
Co-authored-by: vanzue <vanzue@outlook.com>
Co-authored-by: Kai Tao <69313318+vanzue@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/settings-ui/Settings.UI/SerializationContext/SourceGenerationContextContext.cs

@@ -10,7 +10,6 @@ using System.Text.Json.Serialization;
 using System.Threading.Tasks;
 using Microsoft.PowerToys.Settings.UI.Helpers;
 using Microsoft.PowerToys.Settings.UI.Library;
-using SettingsUILibrary = Settings.UI.Library;
 
 namespace Microsoft.PowerToys.Settings.UI.SerializationContext;
 
@@ -24,6 +23,7 @@ namespace Microsoft.PowerToys.Settings.UI.SerializationContext;
 [JsonSerializable(typeof(FileLocksmithSettings))]
 [JsonSerializable(typeof(FindMyMouseSettings))]
 [JsonSerializable(typeof(IList<PowerToysReleaseInfo>))]
+[JsonSerializable(typeof(KeyboardManagerSettings))]
 [JsonSerializable(typeof(LightSwitchSettings))]
 [JsonSerializable(typeof(MeasureToolSettings))]
 [JsonSerializable(typeof(MouseHighlighterSettings))]