OpenCL: Add scaffolding to renderer/vulkan code Start off ANCLE (OpenCL on ANGLE) with backend scaffolding code with placeholder API error returns until they are later implemented. Bug: angleproject:8377 Change-Id: I223d3482cce097ccb298e121fc03ec416e8958fd Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4950556 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>