vulkan: Change mappable buffer memory selection logic

For BufferMapExtendedUsages buffers that are read mappable make it
prefer HOST_CACHED for instead of HOST_COHERENT. This matches the logic
for mappable non-device local buffers already.

For BufferMapExtendedUsages buffers that are write mappable make it
prefer HOST_COHERENT over HOST_COHERENT+HOST_CACHED. This is based on
ARM guidance from [1] and the fact that HOST_CACHED might have overhead
but can't help if there is no CPU read access.

For read+write mappable buffers they still prefer
HOST_COHERENT+HOST_CACHED. If a memory type with both is not available
they will now prefer HOST_CACHED memory over HOST_COHERENT memory.

This also moves all the HOST_CACHED vs HOST_COHERENT logic out of
GetRequiredMemoryPropertyFlags() since neither is actually required.

[1] https://developer.arm.com/documentation/101897/0304/CPU-overheads/Vulkan-CPU-memory-mapping

Bug: 422798184
Change-Id: I2727ad64a3f804257aa74c203ada9ddf3209ffff
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/265474
Reviewed-by: Shahbaz Youssefi <syoussefi@google.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Kyle Charbonneau <kylechar@google.com>