Auto merge of #6218 - ordovicia:alias-check, r=dwijnand

Add `c` alias for `check`

This PR adds `cargo c` alias for `cargo check`.

I believe that one of the most frequently used subcommands is `check`.
Adding this alias would save much time.

Currently, there are three aliases: `b` for `build`, `r` for `run`, `t` for `test`.
I think that adding out-of-the-box `c` alias is *natural* for many developers, and these aliases would cover most of the use cases.
We can add aliases via a configuration file, but I guess people would expect built-in `c` alias along with `b` and others.

One problem I have come up with is that the `clean` subcommand also starts with the letter `c`.
But I believe that running `check` subcommand by mistake would not hurt developers so much.

Fixes #6215