nir: Remove legacy atomics
Depends on !23004 (merged) and !23026 (merged). The organization of this series is as follows:
- Fixes pulled from other MRs.
- Convert a bunch of drivers to be fully unified atomics, instead of unified only in the backend compiler. This wasn't done sooner since it depends on all NIR passes being able to handle unified atomics. At this point, nothing in tree consumes legacy atomics.
- Convert everything to produce unified atomics. At this point, legacy atomics are dead.
- Remove the legacy-to-unified lowering pass, now that it doesn't do anything.
- Remove all references to legacy atomics, they're dead code.
- Remove the legacy atomics themselves, leaving only unified atomics, henceforth known simply as "atomics"
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Edited by Alyssa Rosenzweig