MudFabMenuItem: Fix link rendering when Href is set

[Copilot]

MudFabMenuItem was not behaving like other MudBlazor button-like components when Href was assigned. Instead of rendering as a navigable link, it dropped link-related parameters and remained a non-link button.

• What changed

  • Forward Href, Target, Rel, and related inherited button parameters from MudFabMenuItem to the underlying MudFab.
  • Preserve existing MudFab link behavior so MudFabMenuItem now renders as an anchor when appropriate, including _blank + default noopener handling.

• Behavioral impact

  • MudFabMenuItem now follows the same link semantics as MudButton, MudFab, and similar components.
  • Target, Rel, and anchor rendering work together instead of being silently ignored.

• Regression coverage

  • Add focused tests verifying that a MudFabMenuItem with Href renders as <a> and emits the expected href, target, and rel attributes.

• Example

  <MudFabMenu>
      <MudFabMenuItem Href="https://example.com"
                      Target="_blank"
                      Label="Open docs" />
  </MudFabMenu>

  This now renders the menu item as a clickable anchor and preserves the expected link attributes.