Porting TabbedCommandBar

[niels9001]

This PR brings TabbedCommandBar from the old repository.

Changes:

• New styling inline with WinUI 2.6+
• Resolved a bug where the accent color of a contextual tab wouldn't update on theme change.

The new styling mimics the styling found in the Office apps:

Closes: #93

[Arlodotexe]

@niels9001 Looks like TabbedCommandBar isn't appearing on Wasm. The browser console shows the exception and call stack:

[michael-hawker]

Looks like we should be ensuring to use the WinUI 2 MUX versions of controls everywhere vs. old WUX ones.

[Arlodotexe]

Latest on Wasm - In TabbedCommandBar, text is missing on the tabs and the cause is less clear. No errors in the console.

[Arlodotexe]

I've moved the Wasm issue to a new ticket. We can close this PR once #320 closes and unblocks our CI.