Align rich-text mention listbox implementation behavior

[rajsite]

🧹 Tech Debt

In discussions with @atmgrifter00 in #1912, as part of preventing arbitrary differences between all of our Foundation ListBox implementations (select, combobox, mentions listbox) it was found that the implementation in the mention list box:

1. Does not handle filteredOptions in a way that aligns with the select (as filtering is done the list of options is mutated which state-wise seems unexpected)
2. The mention listbox does not handle the synchronous option registration behavior added to select and combobox in Angular Select placeholder integration #1912.
3. Introduced as part of this PR, the Select will no longer style the "selected" option in the dropdown with the aria-selected attribute, and instead leverage a new active-option attribute. This allows us to keep the aria-selected attribute synchronized with the actual option that is currently representative of the value of the Select. The mentions listbox and combobox should adopt this same pattern (which should result in some CSS moving from the Select styles to the ListOption styles).