Cleanup: correct naming of struct member comments

Also reduce right-shift for DupliGenerator declarations.

source/blender/python/mathutils/mathutils_Color.c

@@ -838,7 +838,7 @@ static PySequenceMethods Color_SeqMethods = {
 };
 
 static PyMappingMethods Color_AsMapping = {
-    /*mp_len*/ (lenfunc)Color_len,
+    /*mp_length*/ (lenfunc)Color_len,
     /*mp_subscript*/ (binaryfunc)Color_subscript,
     /*mp_ass_subscript*/ (objobjargproc)Color_ass_subscript,
 };

source/blender/python/mathutils/mathutils_Euler.c

@@ -649,7 +649,7 @@ static PySequenceMethods Euler_SeqMethods = {
 };
 
 static PyMappingMethods Euler_AsMapping = {
-    /*mp_len*/ (lenfunc)Euler_len,
+    /*mp_length*/ (lenfunc)Euler_len,
     /*mp_subscript*/ (binaryfunc)Euler_subscript,
     /*mp_ass_subscript*/ (objobjargproc)Euler_ass_subscript,
 };

source/blender/python/mathutils/mathutils_Matrix.c

@@ -2977,7 +2977,7 @@ static PySequenceMethods Matrix_SeqMethods = {
 };
 
 static PyMappingMethods Matrix_AsMapping = {
-    /*mp_len*/ (lenfunc)Matrix_len,
+    /*mp_length*/ (lenfunc)Matrix_len,
     /*mp_subscript*/ (binaryfunc)Matrix_subscript,
     /*mp_ass_subscript*/ (objobjargproc)Matrix_ass_subscript,
 };
@@ -3760,7 +3760,7 @@ static PyObject *MatrixAccess_iter(MatrixAccessObject *self)
 }
 
 static PyMappingMethods MatrixAccess_AsMapping = {
-    /*mp_len*/ (lenfunc)MatrixAccess_len,
+    /*mp_length*/ (lenfunc)MatrixAccess_len,
     /*mp_subscript*/ (binaryfunc)MatrixAccess_subscript,
     /*mp_ass_subscript*/ (objobjargproc)MatrixAccess_ass_subscript,
 };

source/blender/python/mathutils/mathutils_Quaternion.c

@@ -1355,7 +1355,7 @@ static PySequenceMethods Quaternion_SeqMethods = {
 };
 
 static PyMappingMethods Quaternion_AsMapping = {
-    /*mp_len*/ (lenfunc)Quaternion_len,
+    /*mp_length*/ (lenfunc)Quaternion_len,
     /*mp_subscript*/ (binaryfunc)Quaternion_subscript,
     /*mp_ass_subscript*/ (objobjargproc)Quaternion_ass_subscript,
 };

source/blender/python/mathutils/mathutils_Vector.c

@@ -2400,7 +2400,7 @@ static PySequenceMethods Vector_SeqMethods = {
 };
 
 static PyMappingMethods Vector_AsMapping = {
-    /*mp_len*/ (lenfunc)Vector_len,
+    /*mp_length*/ (lenfunc)Vector_len,
     /*mp_subscript*/ (binaryfunc)Vector_subscript,
     /*mp_ass_subscript*/ (objobjargproc)Vector_ass_subscript,
 };

source/blender/python/mathutils/mathutils_bvhtree.cc

@@ -1286,7 +1286,7 @@ PyTypeObject PyBVHTree_Type = {
     /*tp_init*/ nullptr,
     /*tp_alloc*/ (allocfunc)PyType_GenericAlloc,
     /*tp_new*/ (newfunc)PyType_GenericNew,
-    /*tp_free*/ (freefunc)0,
+    /*tp_free*/ (freefunc) nullptr,
     /*tp_is_gc*/ nullptr,
     /*tp_bases*/ nullptr,
     /*tp_mro*/ nullptr,