Support constants in patterns (fixes #696) #1000

Job	Run time
runefmt	1m 41s
docs	1m 21s
clippy	1m 39s
rustfmt	6s
basics	1s
msrv	2m 8s
miri_rune_alloc	5m 24s
miri_rune	5m 52s
build_feature (capture-io)	47s
no_default_features	45s
build_feature (cli,doc)	1m 26s
wasm	1m 7s
build_feature (cli,fmt)	1m 20s
no_std_minimal	2m 21s
build_feature (cli)	1m 42s
build_feature (workspace)	48s
build_feature (languageserver)	1m 22s
build_feature (byte-code)	45s
test	10m 37s
	41m 12s

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