inout: add `InOut::into_out` and `InOutBufReserved::into_out` (#1132) #1736

Job	Run time
build (1.41.0, thumbv7em-none-eabi)	18s
build (1.41.0, wasm32-unknown-unknown)	16s
build (stable, thumbv7em-none-eabi)	7s
build (stable, wasm32-unknown-unknown)	11s
test (1.41.0)	16s
test (stable)	10s
minimal-versions / minimal-versions	17s
	1m 35s

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