[HTML5] Editor video driver option. Replace canvas on exit.

Default is "Auto", but can be forced to a specific WebGL version if the
automatic detection fails.

The game and editor canvas are now replaced with a new one in the exit
hooks. This helps the browser do some context cleanup, and allow us to
create a new context of a different type (WebGL/WebGL2).

Enable GLES3/WebGL2 in the Web Editor.

platform/javascript/os_javascript.cpp

@@ -702,14 +702,10 @@ Error OS_JavaScript::initialize(const VideoMode &p_desired, int p_video_driver,
 		set_window_per_pixel_transparency_enabled(true);
 	}
 
-#ifdef TOOLS_ENABLED
-	bool gles3 = false;
-#else
 	bool gles3 = true;
 	if (p_video_driver == VIDEO_DRIVER_GLES2) {
 		gles3 = false;
 	}
-#endif
 
 	bool gl_initialization_error = false;