Migrate to `doc_auto_cfg` #1725

Job	Run time
build (1.65.0, thumbv7em-none-eabi)	4m 40s
minimal-versions	54s
build (1.65.0, wasm32-unknown-unknown)	5m 39s
test (1.65.0)	4m 48s
build (stable, thumbv7em-none-eabi)	10s
test (stable)	33s
build (stable, wasm32-unknown-unknown)	17s
	17m 1s

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