Adopt KHamburgerMenu

The intention here is to hide the menubar by default and show the hamburger menu for new users, but not touch anything for existing users.

Draft because there are a couple of FIXMEs I can't figure out on my own. See the diff view and search for FIXME. Here they are:

• Main toolbar not in the right place (should be on the right, but it stays on the left)
• Spacer in main toolbar not appearing
• Full Screen menu item not appearing
• Some items in KHamburgerMenu cause shortcut conflicts?
• Only want to hide the menubar for new users, not existing users
• Add script to add Hamburger Menu to user's .rc files
• Add KHamburgerMenu to a context menu

BUG: 439895
FIXED-IN: 23.04

@teams/vdg @teams/usability @felixernst