[#12530] Allow header dropdown to be opened with enter key

[domoberzin]

Fixes #12530

Outline of Solution
The current dropdown toggle on the header is created using <a> tags, so currently, the dropdown can actually be toggled using the arrow down key.

This PR changes those <a> tags to use <button>tags also with added classes to reduce any change in the visual appearance. This change will now allow the dropdown to be toggled with the Enter key instead of the arrow key.

This PR also allows tabbing to the Log Out button and fixes #12531 by adding tabindex=0 to the element

[weiquu]

LGTM!

[jasonqiu212]

Thanks for the changes! Just one small nit pick - The buttons seem to flash blue when clicking on it, which I think is different from the original behavior. Is it possible to disable this behavior as well?

Screen.Recording.2023-08-02.at.8.00.03.PM.mov

[domoberzin]

Thanks for the changes! Just one small nit pick - The buttons seem to flash blue when clicking on it, which I think is different from the original behavior. Is it possible to disable this behavior as well?

Screen.Recording.2023-08-02.at.8.00.03.PM.mov

@jasonqiu212 Updated with the behaviour in the video below, which i believe should be similar to the original behaviour, do let me know if any other changes are needed

Screen.Recording.2023-08-03.at.4.35.42.PM.mov

[jasonqiu212]

LGTM!