Implement missing variants of abs/sign This change adds ANGLE support for abs/sign variants introduced in ESSL3. BUG=angle:923 TEST=Unit tests, dEQP tests Unit Tests: TypeTrackingTest.BuiltInAbsSignFunctionFloatResultTypeAndPrecision TypeTrackingTest.BuiltInAbsSignFunctionIntResultTypeAndPrecision dEQP tests passing 100% because of this change: dEQP-GLES3.functional.shaders.builtin_functions.common.abs dEQP-GLES3.functional.shaders.builtin_functions.common.sign Change-Id: I2a3b028611f0eaaac3c031f8926d34a0e146663d Reviewed-on: https://chromium-review.googlesource.com/251491 Reviewed-by: Olli Etuaho <oetuaho@nvidia.com> Tested-by: Olli Etuaho <oetuaho@nvidia.com>