BGL: Workaround broken bgl usage caused by GPU refactor

This directly adress the issues caused by rB536c2e0ec916.

Since the state tracking is done at a lower level, using the bgl
functions needs to be safegarded by the state manager.
The current workaround is to bypass `apply_state` when inside a
callback that used a `bgl` function.

Related to T80730.

This fix T81003.

Also this fix the default blend equation for callbacks.
Fixes T80169 T81289.

source/blender/python/generic/bgl.c

@@ -29,6 +29,8 @@
 #include "BLI_utildefines.h"
 #include "MEM_guardedalloc.h"
 
+#include "GPU_state.h"
+
 #include "../generic/py_capi_utils.h"
 
 #include "glew-mx.h"
@@ -1109,6 +1111,7 @@ static PyObject *Buffer_repr(Buffer *self)
     if (!PyArg_ParseTuple(args, arg_str arg_list, arg_ref arg_list)) { \
       return NULL; \
     } \
+    GPU_bgl_start(); \
     ret_set_##ret gl##funcname(arg_var arg_list); \
     ret_ret_##ret; \
   }