[TIMOB-18260] Override windowWillClose

Resign first responder on windowWillClose
[TIMOB-18260] Override windowWillClose

Cleanup _headerViewProxy and _footerViewProxy on windowWillClose
[TIMOB-18260] Signal windowWillClose before dismissal
Merge pull request #6513 from vishalduggal/timob-18260

CR and FT passed.