fixes #48377

@import and url() link. Fix Microsoft/vscode#29899

Fix #50652 - fix exact setting key search for ui editor. Also fix "new extension" button blinking at the top during search

Settings editor - clear TOC selection when searching. Don't show 'new extension' button when it's filtered out.

And some other fixes

* new mnemonics behavior

* fixing bubbling and mnemonics showing in menus

* updating rendering and removing conflicts with keybindings

* fix submenu dismissal behavior