Add new shader inspection APIs. Each new entry point corresponds to one of the variable types: varyings, attributes, uniforms, output variables, and interface blocks. They return a pointer to the vector with all of the parsed variables, which then the app can copy to its own memory. Currently we do not support the staticUse field in the HLSL translator. BUG=angle:466 Change-Id: I7dc09e761ab070feef5360ad27740110c44853b3 Reviewed-on: https://chromium-review.googlesource.com/208750 Tested-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Zhenyao Mo <zmo@chromium.org> Reviewed-by: Nicolas Capens <capn@chromium.org>