Migrate from `doc_auto_cfg` to `doc_cfg` (#740) #1328

Job	Run time
set-msrv / set-msrv	5s
minimal-versions / minimal-versions	32s
build (1.85.0, thumbv7em-none-eabi)	26s
build (1.85.0, wasm32-unknown-unknown)	20s
build (stable, wasm32-unknown-unknown)	26s
test (stable)	27s
build (stable, thumbv7em-none-eabi)	27s
test (1.85.0)	24s
	3m 7s

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