This ended up being a lot more straight-forward than the menu changes.

TLDR:

• nsMenuBarFrame -> XULMenuBarElement
• nsMenuBarListener -> MenuBarListener

Rest should be rather straight-forward. I didn't want to export
MenuBarListener so moved some of its functions (the access key stuff)
over to LookAndFeel / KeyboardEvent.

This makes the following patch simpler.

Otherwise we leak in some bc tests.

Backed out 2 changesets (5464978a27a8 and d663fc115ab9) for causing multiple leaks.

• Push with failures

• Push with failures after the fix landed

• Failure log for bytes leaked (AbstractWatcher, AsyncFreeSnowWhite, AtomSet, AudioChannelAgent, BackstagePass, ...)

• Failure log for bytes leaked (AbstractWatcher, AnimationTimeline, AsyncFreeSnowWhite, AtomSet, AudioChannelAgent, ...)

• Failure log for SUMMARY: AddressSanitizer: SEGV /builds/worker/workspace/obj-build/dist/include/mozilla/Assertions.h:261:3 in MOZ_Crash

LATER EDIT: there are also multiple failures on browser_siteSpecificWorkArounds.js - Failure log

There are also multiple failures related to browser_blocking<something> which appeared later:
example 1;
example 2;
example 3;
example 4.

And failures on browser_partitionedLocalStorage.js - Failure log

• Backout link

Move accesskey out of nsMenubarListener. r=smaug
https://hg.mozilla.org/mozilla-central/rev/0532ccefaa6f

https://hg.mozilla.org/mozilla-central/rev/5c624797b9cf
https://hg.mozilla.org/mozilla-central/rev/f3a15e75bc39