Modifiers: Add wrapper functions with Mesh / DerivedMesh conversion

Makes the follow changes:

- Add new `deform*` and `apply*` function pointers to `ModifierTypeInfo` that take `Mesh`, and rename the old functions to indicate that they take `DerivedMesh`. These new functions are currently set to `NULL` for all modifiers.
- Add wrapper `modifier_deform*` and `modifier_apply*` functions in two variants: one that works with `Mesh` and the other which works with `DerivedMesh` that is named with `*_DM_depercated`. These functions check which type of data the modifier supports and converts if necessary
- Update the rest of Blender to be aware and make use of these new functions

The goal of these changes is to make it possible to port to using `Mesh` incrementally without ever needing to enter into a state where modifiers don't work. After everything has been ported over the old functions and wrappers could be removed.

Reviewers: campbellbarton, sergey, mont29

Subscribers: sybren

Tags: #bf_blender_2.8

Differential Revision: https://developer.blender.org/D3155

source/blender/editors/object/object_modifier.c

@@ -641,7 +641,7 @@ static int modifier_apply_obdata(ReportList *reports, Depsgraph *depsgraph, Scen
 		BKE_report(reports, RPT_INFO, "Applied modifier only changed CV points, not tessellated/bevel vertices");
 
 		vertexCos = BKE_curve_nurbs_vertexCos_get(&cu->nurb, &numVerts);
-		mti->deformVerts(md, depsgraph, ob, NULL, vertexCos, numVerts, 0);
+		modifier_deformVerts_DM_deprecated(md, depsgraph, ob, NULL, vertexCos, numVerts, 0);
 		BK_curve_nurbs_vertexCos_apply(&cu->nurb, vertexCos);
 
 		MEM_freeN(vertexCos);