wasm: Optimize use of opengles

- USE_WEBGL2 is depreciated, Emscripten now uses MAX_WEBGL_VERSION
- Optimize and remove use of emulated ES2 and ES3, which means
only use WebGL friendly subset.
Users can add USE_ES3=1 and USE_ES2=1 to the final linker arguments
for those respective versions in order to enable using
glDrawArrays and glDrawElements with unbound buffers.
See https://emscripten.org/docs/porting/multimedia_and_graphics/OpenGL-support.html

Pick-to: 6.4
Change-Id: I11ae359966964b3e7aa6e61ccc714c2bfbf61f96
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

cmake/QtWasmHelpers.cmake

@@ -5,7 +5,7 @@ function (qt_internal_setup_wasm_target_properties wasmTarget)
     target_link_options("${wasmTarget}" INTERFACE
     "SHELL:-s ERROR_ON_UNDEFINED_SYMBOLS=1"
     "SHELL:-s EXPORTED_RUNTIME_METHODS=[UTF16ToString,stringToUTF16]"
-    "SHELL:-s USE_WEBGL2=1"
+    "SHELL:-s MAX_WEBGL_VERSION=2"
     "SHELL:-s FETCH=1"
     "SHELL:-s WASM_BIGINT=1")
 
@@ -25,16 +25,6 @@ function (qt_internal_setup_wasm_target_properties wasmTarget)
         target_compile_options("${wasmTarget}" INTERFACE -O2 -msimd128 -msse -msse2)
     endif()
 
-    if (QT_FEATURE_opengles3)
-        target_link_options("${wasmTarget}" INTERFACE "SHELL:-s FULL_ES3=1")
-
-        target_link_options("${wasmTarget}" INTERFACE "SHELL:-s FULL_ES3=1"
-            "SHELL:-s MAX_WEBGL_VERSION=2"
-            "SHELL:-s WEBGL2_BACKWARDS_COMPATIBILITY_EMULATION=1")
-    else()
-        target_link_options("${wasmTarget}" INTERFACE "SHELL:-s FULL_ES2=1")
-    endif()
-
     set(disable_exceptions_catching 1)
     if (QT_FEATURE_exceptions)
         set(disable_exceptions_catching 0)

mkspecs/wasm-emscripten/qmake.conf

@@ -30,9 +30,7 @@ load(emcc_ver)
 
 EMCC_COMMON_LFLAGS += \
     -s WASM=1 \
-    -s FULL_ES2=1 \
-    -s FULL_ES3=1 \
-    -s USE_WEBGL2=1 \
+    -s MAX_WEBGL_VERSION=2 \
     -s ERROR_ON_UNDEFINED_SYMBOLS=1 \
     -s EXPORTED_RUNTIME_METHODS=[UTF16ToString,stringToUTF16] \
     --bind \