Add Value::borrow_any_{ref,mut} to get a typed reference without ownership #927

Job	Run time
runefmt	1m 47s
rustfmt	15s
docs	1m 21s
clippy	1m 57s
basics	1s
miri_rune	5m 29s
miri_rune_alloc	4m 24s
build_feature (capture-io)	55s
msrv	1m 51s
build_feature (cli,doc)	1m 27s
no_default_features	56s
build_feature (cli,fmt)	1m 38s
no_std_minimal	2m 54s
build_feature (cli)	1m 30s
wasm	57s
build_feature (workspace)	51s
build_feature (languageserver)	1m 18s
build_feature (byte-code)	53s
test	10m 55s
	41m 19s

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