Vulkan: Reorder logic in BufferVk::mapRange This CL flattens the logic, ordering read case first, then write, and simpler cases before more complex ones. This is to prepare for an optimization where we ignore certain paths if MAP_UNSYNCHRONIZED_BIT is set. No change in functionality or performance is expected. Bug: angleproject:6680 Change-Id: I0a2e9ee969216c90353eac7af6dabf648dea2173 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/3279615 Commit-Queue: Lingfeng Yang <lfy@google.com> Reviewed-by: Tim Van Patten <timvp@google.com> Reviewed-by: Charlie Lao <cclao@google.com> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org>