Cleanup: Register node property layout callbacks in files

This commit moves the property layout callbacks for node types to their
implementation files from `drawnode.c`. This was proposed a while ago in
T75724.

**Benefits**
 - Fewer files need to be changed when adding a new node.
 - Makes it possible to reuse functions from the node's implementation
   in the layout code.
 - Except for RNA, all of the node "inputs" are in the same place.
 - Code gets shorter overall, avoids the large switch statements.

**Downsides**
 - Requires including two UI headers.
 - Requires adding an editors dependency to the nodes folder.

This commit only changes function nodes and geometry nodes, more can be
moved later.

Differential Revision: https://developer.blender.org/D10352

source/blender/editors/include/UI_interface_icons.h

@@ -23,6 +23,9 @@
 
 #pragma once
 
+/* Required for enum iconSizes which can't be forward declared if this file is included in C++. */
+#include "DNA_ID.h"
+
 #ifdef __cplusplus
 extern "C" {
 #endif
@@ -34,8 +37,6 @@ struct PreviewImage;
 struct Scene;
 struct bContext;
 
-enum eIconSizes;
-
 typedef struct IconFile {
   struct IconFile *next, *prev;
   char filename[256]; /* FILE_MAXFILE size */