Python GPU: Add reference of PyObject GPU object to the GPU object itself

Instead of creating different python wrappers for the same GPU object,
return the same `PyObject` created earlier.

This also allows for more secure access to existing GPU objects.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D11044

source/blender/python/gpu/gpu_py_texture.h

@@ -33,4 +33,5 @@ typedef struct BPyGPUTexture {
 int bpygpu_ParseTexture(PyObject *o, void *p);
 PyObject *bpygpu_texture_init(void);
 
-PyObject *BPyGPUTexture_CreatePyObject(struct GPUTexture *tex) ATTR_NONNULL(1);
+PyObject *BPyGPUTexture_CreatePyObject(struct GPUTexture *tex, bool weak_reference)
+    ATTR_NONNULL(1);