Addition of buffer support for external memory Also adds new end2end tests for these usecases * SubData update * map/unmap buffer * dispatch compute with external buffer Bug: angleproject:5073 Test: ExternalBufferTestES31.*Vulkan Change-Id: Ib3cccaca77b76830effe49d3731782552e7424ec Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2525105 Commit-Queue: Mohan Maiya <m.maiya@samsung.com> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
