Restore editor keyEvent.

This one wasn't fully deprecated (no warning in console, still in documentation) and there
are still a number of extensions that depend upon it.

Revert "Deprecated by adobe/brackets#6787"

This reverts commit 2e7bc6ab049b5fc50915b54f77e8c1c2b1239845.
Merge pull request #9766 from adobe/dangoor/restore-keyevent

Restore editor keyEvent.