Move bitswap to its own crate (#12242)

* Introduce `sc-network-bitswap`

Move the bitswap protocol out of `sc-network` to its own crate.

* Improve test coverage

* Remove mention of bitswap from `sc-network`

* Fix documentation

* Fix clippy and remove the void dependency

* Remove unneeded trait bound and bump prost to 0.11

substrate/client/network/Cargo.toml

@@ -13,9 +13,6 @@ readme = "README.md"
 [package.metadata.docs.rs]
 targets = ["x86_64-unknown-linux-gnu"]
 
-[build-dependencies]
-prost-build = "0.10"
-
 [dependencies]
 async-trait = "0.1"
 asynchronous-codec = "0.6"
@@ -43,7 +40,6 @@ serde_json = "1.0.85"
 smallvec = "1.8.0"
 thiserror = "1.0"
 unsigned-varint = { version = "0.7.1", features = ["futures", "asynchronous_codec"] }
-void = "1.0.2"
 zeroize = "1.4.3"
 fork-tree = { version = "3.0.0", path = "../../utils/fork-tree" }
 prometheus-endpoint = { package = "substrate-prometheus-endpoint", version = "0.10.0-dev", path = "../../utils/prometheus" }