[CmdPal][AOT] Replace CommunityToolkit.MarkdownTextBlock with CommunityToolkit.Lab.MarkdownTextBlock (#39974)

<!-- 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)?
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## Summary of the Pull Request
Why?
The old library doesn't support native AOT. They implement the new one
but still in the lab project.
There are some breaking changes. So, seems we can not 100% to make it
align with the old version.

https://github.com/CommunityToolkit/Labs-Windows/tree/main/components/MarkdownTextBlock

compare:
old:

![image](https://github.com/user-attachments/assets/c2d20d1c-77b8-4bd5-a6e9-45ef30e90ea4)
new:

![image](https://github.com/user-attachments/assets/f65c1acd-ee91-491e-9efd-08ebd191dc58)

old:

![image](https://github.com/user-attachments/assets/129bee49-04c3-4667-88d8-b27718ccd51b)

![image](https://github.com/user-attachments/assets/10c6f845-13ce-4e6b-8fbf-017c8a654fa2)

![image](https://github.com/user-attachments/assets/6f95de3f-e6fb-43a8-9a81-487b20f97f23)

new:

![image](https://github.com/user-attachments/assets/f661731a-efc1-4ffd-86d1-f24cbbe3b9c3)

![image](https://github.com/user-attachments/assets/22cf3e24-f27b-4cef-8e80-352451323bb6)

![image](https://github.com/user-attachments/assets/46719831-905a-450e-b789-93bbedd418bd)

old:

![image](https://github.com/user-attachments/assets/3dd7713a-f5fa-4e1d-90a1-30a518b5df36)

new:

![image](https://github.com/user-attachments/assets/616a176f-a9aa-4f23-9f01-98b30a7c33c4)

old:

![image](https://github.com/user-attachments/assets/5758b51c-44a3-4748-9092-c827009ccc8e)

new:

![image](https://github.com/user-attachments/assets/8deed4cf-e87e-425f-b5a7-61dcab676e45)


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## PR Checklist

- [ ] **Closes:** #xxx
- [ ] **Communication:** I've discussed this with core contributors
already. If 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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## Detailed Description of the Pull Request / Additional comments

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---------

Co-authored-by: Yu Leng <yuleng@microsoft.com>

Directory.Packages.props

@@ -20,6 +20,7 @@
     <PackageVersion Include="CommunityToolkit.WinUI.Extensions" Version="8.2.250402" />
     <PackageVersion Include="CommunityToolkit.WinUI.UI.Controls.DataGrid" Version="7.1.2" />
     <PackageVersion Include="CommunityToolkit.WinUI.UI.Controls.Markdown" Version="7.1.2" />
+    <PackageVersion Include="CommunityToolkit.Labs.WinUI.Controls.MarkdownTextBlock" Version="0.1.250513-build.2126" />
     <PackageVersion Include="ControlzEx" Version="6.0.0" />
     <PackageVersion Include="HelixToolkit" Version="2.24.0" />
     <PackageVersion Include="HelixToolkit.Core.Wpf" Version="2.24.0" />