Finished work on mouse_face_from_buffer_pos for bidi-reordered rows.

Finished work on mouse_face_from_buffer_pos for bidi-reordered rows.
Need lots of testing, including bug#1220.
Next task: get rid of fast_find_position, call mouse_face_from_buffer_pos
instead.

 xdisp.c (rows_from_pos_range): New function.
 (mouse_face_from_buffer_pos): Use it instead of calling
 row_containing_pos for START_CHARPOS and END_CHARPOS.
 (note_mouse_highlight): When bidi reordering is turned on in a
 buffer, call next-single-property-change and
 previous-single-property-change with last argument nil.