Add BoundaryReason::BreakOpportunity flag that will be returned by the
boundaryReasons() when the boundary finder is at the break opportunity
position that might be not an item boundary.
This is the same as (StartWord || EndWord) in Grapheme and Sentence modes;
in Word and Line modes, BreakOpportunity flag might occur between the words
or in between of Line boundaries (e.g. in conjunction with SoftHyphen flag).
In other words, the text boundaries are always break opportunities, but not vice versa.
StartWord and EndWord flags has been deprecated by new StartOfItem and EndOfItem
flags which are not about the word boundaries only. In line breaking,
StartOfItem and EndOfItem are set for the mandatory breaks only.
Change-Id: I79bf297e2b988f5976f30cff0c8ca616385f6552
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>
da7111be51