Multiple toys: Exclude TitleBars from tab navigation (#42030)

## Summary of the Pull Request

This PR removes title bar controls from tab navigation, solving one of
hidden tab stops (the other being #40637).

Affected apps:
- Command Palette - Settings
- Environment Variables
- File Locksmith
- Hosts File Editor
- Registry Preview
- Settings (the search box in the title bar is still tab navigable)

<!-- Please review the items on the PR checklist before submitting-->
## PR Checklist

- [x] Closes: #41944 
- [ ] **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

All apps were manually tests, by pressing tab and shift + tab.

---------

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

src/modules/EnvironmentVariables/EnvironmentVariables/EnvironmentVariablesXAML/MainWindow.xaml

@@ -20,7 +20,7 @@
             <RowDefinition Height="Auto" />
             <RowDefinition Height="*" />
         </Grid.RowDefinitions>
-        <TitleBar x:Name="titleBar">
+        <TitleBar x:Name="titleBar" IsTabStop="False">
             <!--  This is a workaround for https://github.com/microsoft/microsoft-ui-xaml/issues/10374, once fixed we should just be using IconSource  -->
             <TitleBar.LeftHeader>
                 <ImageIcon