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/251491Reviewed-by: Olli Etuaho <oetuaho@nvidia.com>
Tested-by: Olli Etuaho <oetuaho@nvidia.com>