Auto-generate RNA-structs declarations in RNA_prototypes.h

So far it was needed to declare a new RNA struct to `RNA_access.h` manually.
Since 9b298cf3db we generate a `RNA_prototypes.h` for RNA property
declarations. Now this also includes the RNA struct declarations, so they don't
have to be added manually anymore.

Differential Revision: https://developer.blender.org/D13862

Reviewed by: brecht, campbellbarton

source/blender/modifiers/intern/MOD_none.c

@@ -14,6 +14,7 @@
 #include "UI_resources.h"
 
 #include "RNA_access.h"
+#include "RNA_prototypes.h"
 
 /* We only need to define isDisabled; because it always returns 1,
  * no other functions will be called