Make mapv_into_any() work for ArcArray, resolves #1280 #315

Job	Run time
format/nightly	14s
clippy/stable	21s
cross_test/s390x-unknown-linux-gnu/stable	6m 1s
nostd/thumbv6m-none-eabi/stable	16s
cross_test/i686-unknown-linux-gnu/stable	1m 27s
cargo-careful	1m 56s
tests/stable	3m 10s
docs/stable	19s
tests/beta	2m 44s
tests/nightly	3m 11s
tests/1.64.0	3m 54s
conclusion	1s
	23m 34s

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