Fix persistent GL_INVALID_OPERATION spam and resolution-change bugs on Android

- opengl_end_frame() bound framebuffer 0 on Android, which has no valid
  target there (real presentation goes through the OpenXR swapchain's own
  FBOs) - gl4es reported this every frame. Skip it there.
- render_hack_cameras() re-entered opengl_start_frame()/opengl_end_frame()
  for camera-monitor renders that never touch the GL screen; excluded them
  to match use_opengl()'s existing behavior. Also drains a stray error left
  by xrPollEvent().
- ChangeScreenSize() never called opengl_resize() on Android, freezing the
  3D render target at launch size after an in-game resolution change; and
  xr_get_game_resolution() used the swapchain's fixed size instead of the
  current screen resolution, misplacing the laser-pointer cursor after such
  a change.
- Removes all temporary bisection diagnostics added while tracking down the
  GL_INVALID_OPERATION source.

android/app/src/main/cpp/xr_session.h

@@ -74,11 +74,13 @@ void xr_shutdown(void);
 // laser pointer always matches whatever's actually visible.
 void xr_get_game_quad_extent(float *distance_m, float *half_width_m, float *half_height_m);
 
-// Pixel resolution of the game quad's own swapchain - i.e. game_width/
-// game_height as passed to xr_init() (grd_cap->w/h, see Shock.c's
-// InitSDL()) - the logical coordinate space xr_input.c needs to convert a
-// game-quad ray hit's normalized u,v into engine mouse coordinates (see
-// xr_mouse.h).
+// The engine's current screen resolution (gScreenWide/gScreenHigh,
+// InitMac.h) - not the game quad's own swapchain size, which is fixed at
+// launch and never changes - the logical coordinate space xr_input.c needs
+// to convert a game-quad ray hit's normalized u,v into engine mouse
+// coordinates (see xr_mouse.h). Can change at runtime via the in-game
+// options menu (ShockBitmap.c's ChangeScreenSize()), independently of the
+// swapchain.
 void xr_get_game_resolution(int *width, int *height);
 
 #ifdef __cplusplus