bug#70794: 30.0.50; Add Rust compilation regex

[Ergus via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Hi:

Recently working with rust I have noticed that emacs does not recognizes
the rust/cargo error patterns.

Considering that emacs has now the rust-ts-mode, it may worth adding
the rust/cargo error patterns to compile when using that mode

In my system so far I have this:

```
(with-eval-after-load 'rust-ts-mode
  (with-eval-after-load 'compile
    (add-to-list
     'compilation-error-regexp-alist-alist
     `(cargo
       "\\(?:\\(?4:error\\)\\|\\(?5:warning\\)\\):[^\0]+?--> \\(?1:[^:]+\\):\\(?2:[[:digit:]]+\\):\\(?3:[[:digit:]]+\\)"
       1 2 3 (5)
       nil
       (5 compilation-warning-face)
       (4 compilation-error-face)))

    (add-to-list 'compilation-error-regexp-alist 'cargo)))

```

Maybe a more frequent rust user has a more general regex to
recommend. But this one works for me.

WDYT?