Add zero-copy make_mut #637

Job	Run time
loom	1m 54s
minrust	1m 52s
cross (i686-unknown-linux-gnu)	24s
miri	11m 53s
cross (armv7-unknown-linux-gnueabihf)	26s
nightly	3m 5s
cross (powerpc-unknown-linux-gnu)	25s
cross (powerpc64-unknown-linux-gnu)	31s
rustfmt	3s
stable (ubuntu-latest)	1m 19s
cross (wasm32-unknown-unknown)	5s
tsan	2m 26s
stable (macos-latest)	1m 1s
stable (windows-latest)	3m 13s
Publish Documentation	1m 43s
	30m 20s

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