docs: Add csharp markup code example

[eriklimakc]

GitHub Issue (If applicable): #964

PR Type

What kind of change does this PR introduce?

• Documentation content changes

What is the current behavior?

What is the new behavior?

PR Checklist

Please check if your PR fulfills the following requirements:

• [ ] Tested code with current supported SDKs
• [ ] Tested the changes where applicable:
  • [ ] UWP
  • [ ] WinUI
  • [ ] iOS
  • [ ] Android
  • [ ] WASM
  • [ ] MacOS
• [ ] Updated the documentation as needed:
  • [ ] General Doc Update
  • [ ] Controls Doc Update
  • [ ] Extensions Doc Update
  • [ ] controls-styles.md
  • [ ] lightweight-styling.md (LightWeight Styling Resource Keys)
• [ ] Runtime Tests and/or UI Tests for the changes have been added (for bug fixes / features) (if applicable)
• [ ] Contains NO breaking changes
• [ ] Associated with an issue (GitHub or internal)
• [ ] Commits must be following the Conventional Commits specification.

Other information

Internal Issue (If applicable):

[eriklimakc]

I left some TODO comments about stuff I wasn't sure or couldn't find.

• https://github.com/unoplatform/uno.toolkit.ui/blob/41857a5ecb2cf8f954b4d3248170eae907c06d8f/doc/controls/DrawerControl.md?plain=1#L138-L139
• https://github.com/unoplatform/uno.toolkit.ui/blob/41857a5ecb2cf8f954b4d3248170eae907c06d8f/doc/controls/DrawerFlyoutPresenter.md?plain=1#L130-L131
• https://github.com/unoplatform/uno.toolkit.ui/blob/41857a5ecb2cf8f954b4d3248170eae907c06d8f/doc/controls/ExtendedSplashScreen.md?plain=1#L55

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[eriklimakc]

Should I add an "Note" in each page stating that if the person is intending to use C# Markup s/he should install Uno.Toolkit.WinUI.Markup?