Enhance editors notifying input panel for input method changes

Introduced protected QQuickItem::updateInputMethod() and removed
similar, but badly named updateMicroFocus(). Added some missing
notifications from the editors and avoided unnecessary updates when not
having focus.

Change-Id: Id5c00e87dc26fd35c3f919006817511d4ed6418d
Reviewed-by: Andrew den Exter <andrew.den-exter@nokia.com>
Reviewed-by: Joona Petrell <joona.t.petrell@nokia.com>