Cleanup: remove unused includes in Compositor

And move unneeded includes in frequently used headers
to source files.

Slightly reduces compile time.

source/blender/compositor/intern/COM_MemoryProxy.cc

@@ -17,11 +17,8 @@
  */
 
 #include "COM_MemoryProxy.h"
-
 #include "COM_MemoryBuffer.h"
 
-#include "BLI_rect.h"
-
 namespace blender::compositor {
 
 MemoryProxy::MemoryProxy(DataType datatype)