Expose CandidateKind, add srflx/relayed candidate initializers #1328

Job	Run time
lint	39s
cargo-deny (aarch64-apple-ios)	27s
test (ubuntu-latest, stable)	2m 32s
cargo-deny (aarch64-linux-android)	28s
test (ubuntu-latest, beta)	2m 35s
cargo-deny (i686-pc-windows-gnu)	25s
test (ubuntu-latest, 1.65.0)	3m 36s
cargo-deny (i686-pc-windows-msvc)	25s
test (macos-latest, stable)	2m 24s
cargo-deny (i686-unknown-linux-gnu)	30s
test (macos-latest, beta)	3m 28s
cargo-deny (wasm32-unknown-unknown)	25s
test (macos-latest, 1.65.0)	2m 29s
cargo-deny (x86_64-apple-darwin)	25s
test (windows-latest, stable)	4m 40s
cargo-deny (x86_64-apple-ios)	33s
cargo-deny (x86_64-pc-windows-gnu)	31s
test (windows-latest, beta)	3m 40s
cargo-deny (x86_64-pc-windows-msvc)	27s
test (windows-latest, 1.65.0)	4m 37s
cargo-deny (x86_64-unknown-linux-gnu)	25s
cargo-deny (x86_64-unknown-redox)	31s
	36m 12s

Provide feedback