Migrate to `doc_auto_cfg` (#1370) #2025

Job	Run time
build (1.56.0, thumbv7em-none-eabi)	4m 46s
build (1.56.0, wasm32-unknown-unknown)	4m 49s
test (1.56.0)	4m 40s
test (stable)	21s
build (stable, thumbv7em-none-eabi)	23s
build (stable, wasm32-unknown-unknown)	39s
minimal-versions / minimal-versions	56s
	16m 34s

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