config: Rename use_accurate_framebuffers -> use_accurate_gpu_emulation.

- This will be used as a catch-all for slow-but-accurate GPU emulation paths.

src/core/settings.h

@@ -136,7 +136,7 @@ struct Values {
     float resolution_factor;
     bool use_frame_limit;
     u16 frame_limit;
-    bool use_accurate_framebuffers;
+    bool use_accurate_gpu_emulation;
 
     float bg_red;
     float bg_green;