Fix Enhance Mouseover Visuals for TabControl

[corvinsz]

fixes #3802

• Sets the Cursor="Hand" when hovering over a TabItem
• Added the same "hover effect" to TabItem which any normal Button has

Current behavior

New behavior

[jbooth88]

Adding a highlight to the tab header on mouse-hover makes sense. However changing the mouse cursor does not follow the WPF framework defaults for the for tab control. I also checked winforms and winUI, neither change the mouse cursor when hovering over a tab item (provided default styles are applied).

[corvinsz]

I would argue WPF defaults don't matter. The purpose of this library is to bring Material Design to WPF, and the MD specs suggest what is proposed in this PR (as far as i have read it). https://m3.material.io/components/tabs/accessibility#1f5832f9-1898-4da1-bfe4-f40c84027f8a

[corvinsz]

• I added a new attached property called TabAssist.TabHeaderCursor
• The new default Cursor is the Hand
• Consumers can force the old Cursor by setting the AP (e.g.: materialDesign:TabAssist.TabHeaderCursor="Arrow")

[nicolaihenriksen]

I would argue WPF defaults don't matter. The purpose of this library is to bring Material Design to WPF, and the MD specs suggest what is proposed in this PR (as far as i have read it). https://m3.material.io/components/tabs/accessibility#1f5832f9-1898-4da1-bfe4-f40c84027f8a

I agree with @corvinsz. And often when I am in doubt when looking at the MD3 specs, I drop back to the MD2 specs where they have the interactive demos for many things. And that clearly shows the hand cursor on hover: https://m2.material.io/components/tabs#interactive-demo