Cleanup: renaming of GPU contexts for clarity

* opengl_context -> system_gpu_context. This is the operating system OpenGL,
  Metal or Vulkan context provided by GHOST.
* gpu_context -> blender_gpu_context. This is the GPUContext provided by
  the Blender GPU module, which wraps the GHOST context and adds some state.
* Various functions create/destroy/enable/disable both contexts, these have
  just gpu_context in the name now.

@@ -68,2 +67,3 @@
-  GHOST_glDebugContext = (1 << 1),
+  GHOST_gpuStereoVisual = (1 << 0),
+  GHOST_gpuDebugContext = (1 << 1),
 } GHOST_GLFlags;

@@ -231,3 +231,3 @@
    * \param height: The height the window.
    * \param state: The state of the window when opened.
-   * \param glSettings: Misc OpenGL settings.
+   * \param gpuSettings: Misc OpenGL settings.

@@ -78,3 +78,3 @@
    * \param height: The height the window.
    * \param state: The state of the window when opened.
-   * \param glSettings: Misc OpenGL settings.
+   * \param gpuSettings: Misc OpenGL settings.

@@ -104,3 +104,3 @@
    * \param height: The height the window.
    * \param state: The state of the window when opened.
-   * \param glSettings: Misc OpenGL settings.
+   * \param gpuSettings: Misc OpenGL settings.

@@ -169,3 +168,4 @@
+void DRW_gpu_context_disable(void);
 
 #ifdef WITH_XR_OPENXR
 /* XXX: see comment on #DRW_xr_opengl_context_get() */

@@ -3159,3 +3159,3 @@
 {
-  if (G.background && DST.gl_context == NULL) {
+  if (G.background && DST.system_gpu_context == NULL) {
     WM_init_opengl();

@@ -1296,3 +1296,3 @@
 
-  if (engine->wm_gpu_context) {
+  if (engine->wm_blender_gpu_context) {
     /* Activate new OpenGL Context for GPUContext creation. */

@@ -880,41 +880,41 @@ void RE_test_break_cb(Render *re, void *handle, bool (*f)(void *handle))
 /** \name OpenGL Context