webassembly: enable opengl es3

Our WebGL 2 support is half finished, since we use surface format verion of 3
to map to webgl2, but do not enable Open GL ES3 needed for WebGL2 support.

This allows glDrawArrays and glDrawElements to be used

Change-Id: Ifbd434f4d25e49f671145a6727999a90920d6810
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

mkspecs/wasm-emscripten/qmake.conf

@@ -28,6 +28,7 @@ EMTERP_FLAGS = \
 EMCC_COMMON_LFLAGS = \
     -s WASM=1 \
     -s FULL_ES2=1 \
+    -s FULL_ES3=1 \
     -s USE_WEBGL2=1 \
     -s NO_EXIT_RUNTIME=0 \
     -s ERROR_ON_UNDEFINED_SYMBOLS=1 \

src/gui/configure.json

@@ -1315,7 +1315,7 @@
         },
         "opengles3": {
             "label": "OpenGL ES 3.0",
-            "condition": "features.opengles2 && !features.angle && tests.opengles3 && !config.wasm",
+            "condition": "features.opengles2 && !features.angle && tests.opengles3",
             "output": [
                 "publicFeature",
                 { "type": "define", "name": "QT_OPENGL_ES_3" }