Add `BoxTryFuture` and `BoxTryStream` aliases #2715

Job	Run time
cargo bench	20s
cargo clippy	13s
cargo +1.36 build (futures-{core, io, sink})	46s
cargo +stable build	32s
cargo +beta build	25s
cargo doc	17s
cargo +nightly build	22s
cargo hack check --feature-powerset	2m 10s
cargo fmt	5s
cargo minimal-versions build	26s
cargo miri test	41s
cargo build --target thumbv7m-none-eabi	16s
cargo test (ubuntu-latest)	20s
cargo +1.56 build	1m 16s
cargo test (macos-latest)	22s
cargo build --target thumbv6m-none-eabi	17s
cargo test (windows-latest)	42s
cargo test (ubuntu-latest, aarch64-unknown-linux-gnu)	44s
cargo test (ubuntu-latest, armv7-unknown-linux-gnueabihf)	42s
cargo test (ubuntu-latest, armv5te-unknown-linux-gnueabi)	51s
cargo test (ubuntu-latest, i686-unknown-linux-gnu)	38s
cargo test -Z sanitizer=address	50s
cargo test -Z sanitizer=memory	54s
cargo test -Z sanitizer=thread	49s
	14m 58s

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