Since we now have InputCase.uppercase property, use it instead of
InputContext.shift where appropriate.

By using the uppercase property, we ensure any future modification
to ShiftHandler does not break uppercase handling.

The uppercase property is true when either shift or capsLock properties
are true.

Change-Id: I5bdd4431f66619ac944f70273a0a89ba4c750026
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>