Workaround QCompleter issue with closing its popup on escape

QCompleter doesn't close its popup if there's a application wide
'escape' shortcut.
This commit adds the necessary shortcut overrides for CompletingTextEdit
and FancyLineEdit, which fixes the issue at least for find tool bar,
advanced search, gerrit dialog and description field of submit editor.

Task-number: QTCREATORBUG-9453
Change-Id: Ib1df218ab6b9a54fbf19d6132c6edd8e83ace46c
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Eike Ziller <eike.ziller@digia.com>