[x] add a 'cargo xlint' command
[x] add a 'cargo xlint' command

I keep typing this instead of `cargo x lint`.

Closes: #4141
Approved by: sunshowers

aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core