Vulkan:Transform/feedback instanced draw support These fixes allow dEQP 3.1 KHR-GLES31.core.vertex_attrib_binding.basic-input* test cases to pass. This fixes a bug in instanced drawing with transform feedback buffers where we were overwriting the initial transform feedback output as new instances were drawn. To fix this, the vertices in each draw are passed into a uniform value and the output is offset based on the current instance and the number of vertices in the draw. It also fixes a validation error where transform feedback descriptor was sometimes setting a buffer range of 0. This is not allowed, so in the 0 case we pull the actual buffer size from the bufferHelper object. Bug: angleproject:4236 Change-Id: Ib72898a0e6caab96c446c1e996a6124d2c001193 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1979600 Commit-Queue: Tobin Ehlis <tobine@google.com> Reviewed-by: Courtney Goeltzenleuchter <courtneygo@google.com> Reviewed-by: Tobin Ehlis <tobine@google.com>