Fix C-n/C-p inside bidirectional text

Fix C-n/C-p inside bidirectional text

* src/xdisp.c (move_it_by_lines, try_cursor_movement): Handle
glyph rows whose direction of increasing buffer positions is
reverse of the normal: going down in the window makes buffer
positions higher.
* src/indent.c (Fvertical_motion): When looking for the last glyph
row occupied by point, take into account the bidi iteration
direction.