Make TextEdit word selection behaviour consistent.

Word selection initiated by a double click in QTextEdit only selects
a word if the drag point is closer to the end than the start
(assuming ltr selection) which can make it difficult to select small
words with touch input, as such the SelectWords mouseSelectionMode of
TextEdit selected a word if the drag point intersected any part of the
word.  Since we no longer have to retain compability for QTextEdit we
can settle on a single behaviour for word selection.

Change-Id: Iaabb7938a2b61b84a290a9ee41e407c83144b96f
Reviewed-by: Yann Bodson <yann.bodson@nokia.com>