Depsgraph: Re-use evaluated mesh across frames and remove time dependency from all CoW components

This commit is a work forward having less updates during playback, which speeds
things up a lot here. The idea is simple: stop update all copy-on-write
datablocks (which implies full re-evaluation actually) on frame change and
re-use existing evaluated meshes as much as possible.

This brings playback speed to 24 fps on the dino test scene here. Performance
drops down a lot when armature is animated tho, but that's because of need of
tangent space calculation which we can't do much about from just a dependency
graph.

Hopefully this doesn't make copy-on-write too unstable, quick tests here are
surviving fine.

source/blender/depsgraph/intern/builder/deg_builder_nodes.h

@@ -107,7 +107,7 @@ struct DepsgraphNodeBuilder {
 
 	void begin_build(Main *bmain);
 
-	IDDepsNode *add_id_node(ID *id);
+	IDDepsNode *add_id_node(ID *id, bool do_tag = true);
 	TimeSourceDepsNode *add_time_source();
 
 	ComponentDepsNode *add_component_node(ID *id,
@@ -206,6 +206,7 @@ struct DepsgraphNodeBuilder {
 protected:
 	Main *m_bmain;
 	Depsgraph *m_graph;
+	GHash *m_cow_id_hash;
 };
 
 }  // namespace DEG