Improve illegal crate name importation error message

[csmoe]

error: expected one of `;` or `as`, found `-`
 --> src/main.rs:1:17
  |
1 | extern crate foo-bar;
  |                 ^ expected one of `;` or `as` here

error: aborting due to previous error

error: Could not compile `hello`.

To learn more, run the command again with --verbose.

it'll be better to suggest using snake name here:

error: found illegal crate name
 --> src/main.rs:1:17
  |
1 | extern crate foo-bar;
  |              ^^^^^^^ consider changing this to: `foo_bar`

error: aborting due to previous error

error: Could not compile `hello`.

To learn more, run the command again with --verbose.

[estebank]

Duplicate of #48437. We should not only provide the suggestion, the compiler should continue compiling and if the rest of the code is correct, no other errors should be emitted.