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>