[HTML5] Add WebGL2 (GLES3) support using the OpenGL renderer.

Note, the editor build requires the mbedtls module to be manually
enabled, as it is currently needed as a ResourceUID dependency.

This will need to be addressed in a separate PR.

drivers/SCsub

@@ -25,10 +25,9 @@ SConscript("winmidi/SCsub")
 # Graphics drivers
 if env["vulkan"]:
     SConscript("vulkan/SCsub")
-    SConscript("gles3/SCsub")
+if env["opengl3"]:
     SConscript("gl_context/SCsub")
-else:
-    SConscript("dummy/SCsub")
+    SConscript("gles3/SCsub")
 
 # Core dependencies
 SConscript("png/SCsub")