Made it so dynamic topology will flush changes from
SculptSession->bm to Object->me.
Used the same approach as sculptsession_bm_to_me does,
but instead of using DAG_id_tag_update used in-place
DerivedMesh release. Otherwise this lead to some
update issues resulting in missed object after render.
Also fixed multires modifier not being applied for
render when rendering from dyntopo sculpt mode.
P.S. Apparently sculpsession_bm_to_me was declared
in BKE_paint.h but implemented in object.c.
Rather confusing and better make it so this
functions are declared and implemented in
consistent files. But will solve this in a
separate commit.
4fcd44d389