Removing WCT 7.x references (#41733)

## Summary of the Pull Request

This PR introduces the following changes:
- Replace the MarkdownTextBlock with the latest version in
CommunityToolkit Labs, and removing the 7.x version.
- Replacing WrapPanel from 7.x with the 8.0 version.
- Replacing converters from 7.x with the 8.0 version.
- Remove unused namespaces related to the Toolkit

No visual or behavior changes, except for the release notes that now
look better :):

Before:
<img width="678" height="906" alt="image"
src="https://github.com/user-attachments/assets/8b3ac267-b4cd-499c-8e16-d8420a176a4a"
/>


After:
<img width="846" height="881" alt="image"
src="https://github.com/user-attachments/assets/cb4f2d85-0c23-4263-80d6-28c2ab403704"
/>


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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

<!-- 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

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wherever possible, but list manual validation steps taken as well -->
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---------

Co-authored-by: Gordon Lam <73506701+yeelam-gordon@users.noreply.github.com>
Co-authored-by: Gordon Lam (SH) <yeelam@microsoft.com>

src/settings-ui/Settings.UI/SettingsXAML/OOBE/Views/OobeMeasureTool.xaml

@@ -5,7 +5,7 @@
     xmlns:controls="using:Microsoft.PowerToys.Settings.UI.Controls"
     xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
     xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
-    xmlns:tk7controls="using:CommunityToolkit.WinUI.UI.Controls"
+    xmlns:tkcontrols="using:CommunityToolkit.WinUI.Controls"
     mc:Ignorable="d">
 
     <controls:OOBEPageControl x:Uid="Oobe_MeasureTool" HeroImage="ms-appx:///Assets/Settings/Modules/OOBE/ScreenRuler.gif">
@@ -15,7 +15,7 @@
 
                 <controls:ShortcutWithTextLabelControl x:Name="HotkeyActivation" x:Uid="Oobe_MeasureTool_Activation" />
 
-                <tk7controls:MarkdownTextBlock x:Uid="Oobe_MeasureTool_HowToLaunch" Background="Transparent" />
+                <tkcontrols:MarkdownTextBlock x:Uid="Oobe_MeasureTool_HowToLaunch" />
 
                 <StackPanel Orientation="Horizontal" Spacing="8">
                     <Button x:Uid="OOBE_Settings" Click="SettingsLaunchButton_Click" />