GetMemoryType was a bare first-superset match that threw whenever no
memory type satisfied the requested property flags. Callers combining a
mandatory flag with a perf-only one (HOST_VISIBLE | DEVICE_LOCAL for the
descriptor heaps) would then fail allocation on any device without a
host-visible device-local heap (no resizable BAR).
It now takes a `preferred` mask distinct from `required`: a type
satisfying both is chosen first, falling back to a required-only match
when the preference is unavailable, and throwing only when even
`required` cannot be met. VulkanBuffer::Create/Resize gain an optional
trailing `preferredPropertyFlags`, and the descriptor heaps now treat
DEVICE_LOCAL as a preference on top of mandatory HOST_VISIBLE.
This does not touch any flush/barrier behaviour — coherency is not
assumed anywhere here.
Adds tests/MemoryTypeFallback, a pure-CPU test that installs synthetic
memory layouts and exercises selection, preference, fallback, and the
unsatisfiable-required throw.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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