Implement float-integer conversions for ESSL 3.00 The implementation uses asint, asuint and asfloat in the HLSL output. BUG=angle:865 Change-Id: I6b48298e18c7b3b0bdeac522b375ebc4eab7cf4e Reviewed-on: https://chromium-review.googlesource.com/239520 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org> Tested-by: Olli Etuaho <oetuaho@nvidia.com>