Symbol key acts as modifier key

On a device that has distinct multi-touch panel, pressing '123?' key
will change keyboard layout to symbol mode.  While pressing '123?'
key, you can press other symbol key to input.  Then releasing '123?'
key will change keyboard layout back to alphabet mode.

Bug: 2973383
Change-Id: I3b069fb19141820def8060db4766a08c7c0a6ff0