Emulate tanh on HLSL This ensures mathematically correct results on large inputs. BUG=chromium:795269 BUG=angleproject:1093 TEST=dEQP-GLES3.functional.shaders.builtin_functions.precision.tanh* Change-Id: Id5ba05a3284e51a34f196b419abef0f4a41551e0 Reviewed-on: https://chromium-review.googlesource.com/832463 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>