Notify when the TextInput cursorRectangle property changes within pre-edit

Notify when the TextInput cursorRectangle property changes within pre-edit

Anything that updates the horizontal scroll is also likely to change the
position of the cursor rectangle and the micro focus.  So group these
actions together and ensure they're done before emitting
cursorPositionChanged() so positionToRectangle() returns a valid value
from that handler.

Change-Id: I5fadc58efb148a8dabe88a94381c86cd64dba3bd
Task-number: QTBUG-19089
Reviewed-by: Martin Jones
(cherry picked from commit a0b2fc44ff8752193cacde52276b1822741f5374)