zink: improve depth buffer elimination/layout handling
in many cases (e.g., manhattan_31 and pubg traces) a depth attachment is bound to both framebuffer (for depth test only) and as a sampler (read-only). instead of using GENERAL or FEEDBACK_LOOP layout here, it's much, much, much better to use ZS_READ_ONLY, as that avoids losing compression.
getting it done just requires some minor tweaks to existing renderpass layout handling to trigger recalc at the right time
~20% perf boost in manhattan_31 and 10-15% in pubg on ICL