Vulkan: Add test for Pixel bug with passthrough GLSL function Passing in a sampler2D's values using texture2D through a function generates unexpected results on a Pixel device with the Vulkan backend. 1. SamplerPassthroughFailedLink - program fails to link. 2. SamplerPassthroughIncorrectColor - output color is incorrect. These tests have no issues with SwiftShader ICD. Tests: angle_end2end_tests --gtest_filter=*SamplerPassthrough*Vulkan* Bug: angleproject:5457 Change-Id: I9c43062e98c7b3637bb8a2b00a957141da821f0a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2586059 Commit-Queue: Cody Northrop <cnorthrop@google.com> Reviewed-by: Cody Northrop <cnorthrop@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>