Allow submenus in Twenty Twenty to be dismissed using the `esc` key to meet WCAG 1.4.13. Set focus to previous submenu parent on `esc`, and ensure that after escaping the last submenu, tab moves to the next parent item, not back into the submenu.
Props lcarevic, rcreators, pratiklondhe, poena, karmatosed, chaion07, audrasjb, mehdi01, mohonchandra, najmulsaju, saurabhdhariwal, ugyensupport, shailu25.
Fixes#49950.
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