cpal

Support ScreenCapture loopback #939

Job	Run time
ubuntu-test	34s
clippy-test	51s
asmjs-wasm32-test (wasm32-unknown-emscripten)	1m 1s
rustfmt-check	9s
cargo-publish	0s
wasm32-bindgen-test (wasm32-unknown-unknown)	23s
wasm32-wasi-test (wasm32-wasi)	23s
windows-test (x86_64)	3m 20s
android-apk-build	1m 45s
windows-test (i686)	3m 30s
android-check	39s
ios-build	2m 0s
linux-check-and-test-armv7	1m 32s
macos-test	1m 28s
wasm-beep-build	36s
	18m 11s

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