Vulkan: Move some bufferRead logic into CommandBufferHelperCommon Some of the logic of bufferRead is common, to avoid code duplication, it has been refactored into bufferReadImpl and moved into CommandBufferHelperCommon. Bug: b/282194402 Change-Id: I98cd0788db7fe9f14bd3155b28dc208f9f4a138a Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/4581061 Reviewed-by: Roman Lavrov <romanl@google.com> Commit-Queue: Charlie Lao <cclao@google.com>