Add simulcast sending support #2133

Job	Run time
lint	55s
test_wincrypto (windows-latest, stable)	3m 20s
cargo-deny (aarch64-apple-ios)	21s
test (ubuntu-latest, stable)	1m 41s
test_wincrypto (windows-latest, beta)	2m 43s
cargo-deny (aarch64-linux-android)	20s
test (ubuntu-latest, beta)	1m 47s
test_wincrypto (windows-latest, 1.71.1)	2m 47s
cargo-deny (i686-pc-windows-gnu)	22s
test (ubuntu-latest, 1.71.1)	2m 6s
cargo-deny (i686-pc-windows-msvc)	21s
test (macos-latest, stable)	1m 26s
cargo-deny (i686-unknown-linux-gnu)	20s
test (macos-latest, beta)	1m 38s
cargo-deny (wasm32-unknown-unknown)	20s
test (macos-latest, 1.71.1)	1m 33s
cargo-deny (x86_64-apple-darwin)	18s
test (windows-latest, stable)	3m 52s
cargo-deny (x86_64-apple-ios)	18s
test (windows-latest, beta)	3m 9s
cargo-deny (x86_64-pc-windows-gnu)	23s
test (windows-latest, 1.71.1)	3m 35s
cargo-deny (x86_64-pc-windows-msvc)	20s
cargo-deny (x86_64-unknown-linux-gnu)	20s
cargo-deny (x86_64-unknown-redox)	20s
	34m 35s

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