Enable gsampler2dMS, texelFetch, textureSize in glslang in
es 3.0 if ANGLE_texture_multisample is supported.

Bug: angleproject:2275
TEST=SamplerMultisampleEXTTest.TextureMultisampleEXTEnabled

Change-Id: Ibfa367970db3ae790f3822e57eb50090843dc6db
Reviewed-on: https://chromium-review.googlesource.com/c/867521Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Yizhou Jiang <yizhou.jiang@intel.com>