IE9: evt.charOrCode set incorrectly for ESCAPE key

[bill]

See test_TooltipDialog.html. Open first dialog and then press ESCAPE key to close the dialog. On IE9, it has no effect.

For dojo normalized events, evt.charOrCode should be set to 27 for the ESCAPE key. However, on IE9, it's set to a character instead. Thus our existing code that checks evt.charOrCode doesn't realize it's the ESCAPE key.

The problem is in event.js: _setKeyChar() depends on evt.charCode being 0/null/""/etc., but on IE9 it's a valid character.

[bill]

Got double-submitted, closing as dup of #12495.