Rename Layout to LayoutBitset #578

Job	Run time
Pass MSRV values to other jobs	3s
clippy/stable	16s
miri	10m 55s
docs/nightly	20s
cross_test/i686-unknown-linux-gnu/stable	1m 52s
cargo-careful	1m 41s
nostd/thumbv6m-none-eabi/stable	12s
cross_test/s390x-unknown-linux-gnu/stable	7m 14s
format/nightly	17s
blas-msrv	44s
tests/beta	2m 20s
tests/1.64.0	3m 28s
tests/nightly	2m 40s
tests/stable	2m 27s
conclusion	3s
	34m 32s

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