Add a personal menu dropdown that opens on clicking user avatar icon
in navbar added in previous commit.
The args passed to render_personal_menu() in onShow() are returned by
get_personal_menu_content_context() in popover_menus_data.js so that
they can be unit tested.
Additionally, added CSS to get a custom arrow for dropdown menu.
Added a `?` hotkey in keyboard shortcuts option in personal_menu
dropdown in a style similar to our tooltip's hotkey by adding
? in a span with class .tooltip-hotkey-hint and adding some CSS.
Fixes part of #22802.
Hardik Dharmani