* Remove dtolnay's rust-toolchain action
I believe our rust-toolchain.toml handles its use case exactly.
I don't believe this'll work, as it'd require rustup install a cargo stub
before any toolchain is installed, yet I want to confirm it doesn't.
* Place quotes around nightly toolchain version
* Put toolchain before options to resolve what appears to be a bug in rustup's help strings
* Add wasm32-unkknown-unknown to clippy workflow
Adds a Rust toolchain file to be less disruptive to developers who don't keep
their toolchain synchronized (by now having rustup automatically synchronize).
Hopefully helps resolve how +nightly clippy may pass for the coordinator, yet
building would fail due to stable's (hopefully prior?) failure to model some
async functions re: Send/Sync.
Also adds rust-src as a component in preparation of
https://github.com/paritytech/polkadot-sdk/pull/2217
* Move to dtolnay/toolchain
* Correct dtolnay/toolchain to rust-roolchain
* Pass toolchain by argument instead of revision
Introduces malleability by referring to HEAD of dtolnay, yet GHA errored on the
prior syntax.
