Stop creating legacy layout boxes for menus/menulists/menuitems.

Move all the event handling stuff to the DOM.

Backed out for failures on test_submenuClose.xhtml and nsMenuPopupFrame.cpp

• backout: https://hg.mozilla.org/integration/autoland/rev/ff7a5a98e2efc854df61d41aca9056a718c05f0f
• push: https://treeherder.mozilla.org/jobs?repo=autoland&group_state=expanded&selectedTaskRun=IlGmPc_hRT2g5BqF0NEToQ.0&revision=f11c529b240799df93c4dd8c17ecd8636f9b10de
• failure logs:
  • TEST-UNEXPECTED-FAIL | layout/xul/test/test_submenuClose.xhtml | Test timed out. -
  • builds/worker/checkouts/gecko/layout/xul/nsMenuPopupFrame.cpp:2042:5: error: unknown type name 'KeyboardEvent'; did you mean 'mozilla::dom::KeyboardEvent'?

Also failing on:

• PROCESS-CRASH | toolkit/content/tests/chrome/test_edit_contextmenu.html | application crashed [@ mozilla::dom::BrowsingContext::CanAccess(mozilla::dom::BrowsingContext*, bool)]
• TEST-UNEXPECTED-FAIL | devtools/client/storage/test/browser_storage_delete_usercontextid.js | Test timed out -

This test passes on automation, somehow, probably due to timing.
Locally the click rolls up the popup (so you'd need a second click to
show the other popup).

This happens both with and without the patch, and given I debugged and
it is trivial to fix, well, make sure to hide the previously open menu
before clicking on another...

https://hg.mozilla.org/mozilla-central/rev/47c002d36372

https://hg.mozilla.org/mozilla-central/rev/7b8542b7c655