Fix fuzzer nondeterminism#8886
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Fixes #8770. The fuzzer was non-deterministic across architectures since we had two calls to
pick()in the arguments tomakeAtomicRMW, so the evaluation order of the twopickcalls was non-deterministic. Fix this by pulling the function calls outside of the arguments ofmakeAtomicRMW.Also increase the fuzz metrics test seed file size (2214 bytes -> 1020 KB) to increase the likelihood of catching similar issues in CI, and exercise more instructions in the test. This bug wasn't caught by CI in #8253.
Tested by basing #8885 on top of this which failed previously due to the non-determinism, and now succeeds.