Add a `WebRtcFraming` utility for WebRTC messages #4019

Job	Run time
check-no-std	1m 40s
check-features	3m 15s
cargo-spellcheck	25s
cargo-deny (bans licenses sources)	30s
check-rustdoc-links	49s
clippy	45s
fmt	32s
fuzzing-binaries-compile	4m 44s
test-32bits	6m 2s
test-64bits	6m 21s
wasm-node-check	1m 58s
wasm-node-versions-match	31s
all-ci	1s
	27m 33s

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