[MAUI Blazor] Improved NavBar + refactoring

[veler]

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• New feature or enhancement
• UI change (please include screenshot!)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Internationalization and localization
• Other (please describe):

What is the current behavior?

• Theme update wasn't supported.
• NavBar wasn't taking consideration of user's preference regarding whether the pane should be collapsed or expanded.
• NavBar group items would take too much height when expanded.
• Some NavBar colors, size and animation were off compared to WinUI.

What is the new behavior?

• More consistent UI with WInUI. For example, items in NavBar are now consistent with WinUI's NavigationViewItem.
• Scrollbar are now invisible by default, visible on mouse hover, enlarged when the mouse cursor is near the scrollbar.
• Button theme is now consistent with WinUI.
• Got rid of FluentUI Blazor library. If needed, we can still pump the styles from it.
• Got rid of some code that wasn't used.
• Large refactoring in overall.

Below is Before/After comparison.

Untitled.Project.mp4

Quality check

Before creating this PR:

• Did you follow the code style guideline as described in CONTRIBUTING.md
• Did you build the app and test your changes?
• Did you check for accessibility? On Windows, you can use Accessibility Insights for this.
• Did you verify that the change work in Release build configuration
• Did you verify that all unit tests pass
• If necessary and if possible, did you verify your changes on:
  • Windows
  • macOS (DevToys 2.0)
  • Linux (DevToys 2.0)