[scopes] Enable keyboard typing/spelling suggestion in scopes search field

Status changed to 'Confirmed' because the bug affects multiple users.

This was originally disabled because predictive text did not play well with the search engine, we need to find out if that was resolved since.

Text in the preedit buffer isn't reported alongside committed text for Qt widgets, it might be possible to work around this for the scopes by listening to QInputMethodEvents (which will include incoming changes to the preedit buffer); alternatively a more general fix would be to somehow get all Qt input widgets to report preedit text alongside committed text (which would solve this in other scenarios as well). I'm not certain if this would need to be done via a change to Qt itself or if its possible at the UITK level.

My two cents is you do not want the osk style of word prediction. Scopes have the opportunity to do a much better job based on the context. For example when searching the store if I type "podbrid" it should find "podbird". The scope could do this, the osk could not and would suggest "tripod"

unity8 waiting for design -> Incomplete