As noted in rB9a69c456bd85, the do_clip option of
ED_view3d_win_to_3d_on_plane can be misleading since it does not
consider clip_start and clip_end.
This is especially bad for orthographic view since clip_start in this
case is negative.
This patch proposes to retrieve the values of clip_start and clip_end
through winmat and use them to peform a most expected do_clip.
NOTE: Functions that check whether rv3d->is_persp for do_clip can be updated after this.
NOTE: as noted in rBcf6be711e2a0, plane aligned is another thing that should be fixed in ED_view3d_win_to_3d_on_plane