All crates should have a consistent API & naming

[thomaseizinger]

Discussed in #2174.

Summary:

Rename symbols within libp2p- sub crates such that they can best be references via the module that is re-exported from the libp2p meta-crate. For example:

use libp2p::ping;

let behaviour = ping::Behaviour::new(ping::Config::default());

Crates

• Revise naming of libp2p-ping symbols #2215
• protocols/ping: Properly deprecate types with Ping prefix #2937
• protocols/identify: Revise symbol naming #2927
• transports/tcp: Unify symbol naming #2961
• refactor(request-response): revise public API to follow naming convention #3159
• refactor(relay): revise public API to follow naming convention #3238
• refactor(dcutr): reshape public API to follow naming guidelines #3214
• mdns: update if-watch to 3.0.0 #3096
• refactor(gossipsub): revise symbol naming to follow conventions #3303
• feat(yamux): rename symbols to follow module-based naming convention #3852
• feat(noise): deprecate all handshake patterns apart from XX #3768
• refactor(plaintext): rename symbols to follow naming convention #4535
• kad: rename to follow naming convention across repository #4485
• dns: rename to follow naming convention across repositry #4486
• chore(floodsub): change naming conventions #5855
• chore(mplex): Changing naming convention #5870
• chore(websocket): change name convention #5873
• libp2p-uds:

[thomaseizinger]

I followed the same approach outlined here in #2859 and introduced top-level dummy and keep_alive modules in libp2p-swarm. I think eventually, it would be great if we can also introduce these top-level modules in libp2p and re-export these kind of modules there. That would allow us to group things like dummy::Behaviour and dummy::ConnectionHandler together under libp2p::dummy which would be consistent with the re-export of sub-crates like libp2p::ping or libp2p::kad.