util: move UTF-8 decoding to its own module #472

Job	Run time
test (stable, ubuntu-latest, stable)	5m 39s
test (beta, ubuntu-latest, beta)	5m 41s
msrv	52s
test (nightly, ubuntu-latest, nightly)	3m 42s
rustfmt	13s
cross (i686-unknown-linux-gnu)	1m 8s
test (macos, macos-latest, stable)	3m 26s
cross (aarch64-unknown-linux-gnu)	1m 25s
testbench	1m 2s
test (win-msvc, windows-latest, stable)	3m 46s
cross (powerpc-unknown-linux-gnu)	1m 25s
wasm32-unknown-emscripten	1m 34s
cross (powerpc64-unknown-linux-gnu)	1m 25s
wasm32-unknown-uknown	26s
cross (s390x-unknown-linux-gnu)	1m 48s
wasm32-wasip1	53s
win-gnu	1m 40s
	36m 5s

Provide feedback