Rename Layout to LayoutBitset #576

Job	Run time
cross_test/i686-unknown-linux-gnu/stable	34s
Pass MSRV values to other jobs	4s
cargo-careful	1m 0s
format/nightly	12s
clippy/stable	13s
cross_test/s390x-unknown-linux-gnu/stable	42s
miri	11m 16s
nostd/thumbv6m-none-eabi/stable	11s
docs/nightly	21s
tests/beta	22s
tests/1.64.0	22s
tests/nightly	25s
blas-msrv	27s
tests/stable	19s
conclusion	0s
	16m 28s

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