GPU Python: Use 'PyC_ParseStringEnum' to parse items

Currently the GPU module for python has different ways to handle enums.
- Organizing items in `PyC_StringEnumItems` arrays and parsing them with `PyC_ParseStringEnum`.
- Using dedicated functions for each type of enum (`bpygpu_ParsePrimType`, `pygpu_ParseVertCompType` and `pygpu_ParseVertFetchMode`).

Although apparently more efficient (especially `pygpu_ParseVertCompType`
which transforms strings into integers for simple comparison), these
dedicated functions duplicate functionality, increase the complexity of
the code and consequently make it less readable.

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D10456

source/blender/python/gpu/gpu_py.c

@@ -23,6 +23,7 @@
 
 #include <Python.h>
 
+#include "GPU_primitive.h"
 #include "GPU_texture.h"
 
 #include "../generic/py_capi_utils.h"
@@ -30,9 +31,23 @@
 #include "gpu_py.h" /* own include */
 
 /* -------------------------------------------------------------------- */
-/** \name GPU Module
+/** \name GPU Enums
  * \{ */
 
+struct PyC_StringEnumItems bpygpu_primtype_items[] = {
+    {GPU_PRIM_POINTS, "POINTS"},
+    {GPU_PRIM_LINES, "LINES"},
+    {GPU_PRIM_TRIS, "TRIS"},
+    {GPU_PRIM_LINE_STRIP, "LINE_STRIP"},
+    {GPU_PRIM_LINE_LOOP, "LINE_LOOP"},
+    {GPU_PRIM_TRI_STRIP, "TRI_STRIP"},
+    {GPU_PRIM_TRI_FAN, "TRI_FAN"},
+    {GPU_PRIM_LINES_ADJ, "LINES_ADJ"},
+    {GPU_PRIM_TRIS_ADJ, "TRIS_ADJ"},
+    {GPU_PRIM_LINE_STRIP_ADJ, "LINE_STRIP_ADJ"},
+    {0, NULL},
+};
+
 struct PyC_StringEnumItems bpygpu_dataformat_items[] = {
     {GPU_DATA_FLOAT, "FLOAT"},
     {GPU_DATA_INT, "INT"},