Translator: Fixed textureGatherOffsets validation The parser only considered the case where the input to the textureGatherOffsets() function is an aggregate constructor node, but not if it is a pre-initialized constant variable. Added code to handle the constant variable case. Tests:KHR-GLES32.core.gpu_shader5.texture_gather_offsets_color KHR-GLES32.core.gpu_shader5.texture_gather_offsets_depth Bug: angleproject:5362 Change-Id: Ib1dd3450071341082ea6f0f2a243c3bb3ef6b95a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3217852 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Brandon Schade <b.schade@samsung.com>