PyAPI: include the property name & type in registration errors

This gives useful context in errors,
also remove newline endings from exceptions.

source/blender/python/intern/bpy_props.h

@@ -33,7 +33,10 @@ StructRNA *pointer_type_from_py(PyObject *value, const char *error_prefix);
 
 typedef struct {
   PyObject_HEAD
-  /* This isn't GC tracked, it's a function from `bpy.props` so it's not going away. */
+  /**
+   * Internally a #PyCFunctionObject type.
+   * \note This isn't GC tracked, it's a function from `bpy.props` so it's not going away.
+   */
   void *fn;
   PyObject *kw;
 } BPy_PropDeferred;