Define a struct-level `#[safety_constraint(...)]` attribute #7262

Job	Run time
benchcomp-tests	4m 8s
documentation	2m 7s
perf	32m 14s
regression (macos-13)	11m 55s
write-json-symtab-regression	13m 16s
regression (ubuntu-20.04)	11m 53s
regression (ubuntu-22.04)	11m 54s
regression (macos-14)	11m 37s
	1h 39m 4s

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