RNA: Generate property declerations header, solving msg-bus C++ incompatibility

Lets `makesrna` generate a `RNA_prototypes.h` header with declarations for all
RNA properties. This can be included in regular source files when needing to
reference RNA properties statically.

This solves an issue on MSVC with adding such declarations in functions, like
we used to do. See 800fc17367. Removes any such declarations and the related
FIXME comments.

Reviewed By: campbellbarton, LazyDodo, brecht

Differential Revision: https://developer.blender.org/D13837

source/blender/python/intern/CMakeLists.txt

@@ -18,6 +18,8 @@ set(INC
   ../../../../intern/guardedalloc
   ../../../../intern/mantaflow/extern
   ../../../../intern/opencolorio
+  # RNA_prototypes.h
+  ${CMAKE_BINARY_DIR}/source/blender/makesrna
 )
 
 set(INC_SYS
@@ -357,3 +359,6 @@ if(WITH_HARU)
 endif()
 
 blender_add_lib(bf_python "${SRC}" "${INC}" "${INC_SYS}" "${LIB}")
+
+# RNA_prototypes.h
+add_dependencies(bf_python bf_rna)