Enhancement: Add search icon functionality to dropdowns

[erbanku]

Description of the new feature

Currently, dropdowns menus in Windows Terminal lack a search icon/functionality, making it difficult to quickly locate items, especially in long lists.

See attached screenshot for example:

Adding a search input box to these menus would improve usability and speed up navigation.

Proposed technical implementation details

Integrate a search input box at the top of dropdown menus

[zadjii-msft]

I suppose those could be AutoSuggestBox's, so long as we can have them expanded by default.