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.

• uno.toolkit.ui/doc/controls/DrawerControl.md

  Lines 138 to 139 in 41857a5

  	//TODO Couldnt find Drawer Style
  	.Style(Theme.NavigationView.Styles.Drawer)

• uno.toolkit.ui/doc/controls/DrawerFlyoutPresenter.md

  Lines 130 to 131 in 41857a5

  	//TODO couldn't find BottomDrawer style
  	.FlyoutPresenterStyle(Theme.FlyoutPresenter.Styles.BottomDrawer)

• uno.toolkit.ui/doc/controls/ExtendedSplashScreen.md

  Line 55 in 41857a5

  .Platforms(//TODO how to add multiple choices?)

[github-actions]

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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?