Add `.shrink_to_fit()` for `Array` #264

Job	Run time
nostd/thumbv6m-none-eabi/stable	15s
tests/stable	2m 29s
cargo-careful	1m 49s
tests/beta	2m 33s
clippy/stable	15s
cross_test/s390x-unknown-linux-gnu/stable	4m 50s
tests/nightly	2m 31s
cross_test/i686-unknown-linux-gnu/stable	1m 27s
docs/stable	14s
format/nightly	11s
tests/1.64.0	3m 46s
conclusion	1s
	20m 21s

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