better error when a keyword is used as identifier

[mimoo]

imagine that we try to create a struct with a field called pub:

struct Thing {
  pub: Field
}

this won't work as pub is a reserved keyword:

Error:   × Looks like something went wrong in parser
   ╭─[tmp/src/main.no:3:1]
 3 │ struct Thing {
 4 │   pub: Field
   ·   ─┬─
   ·    ╰── here
 5 │ }
   ╰────
  help: invalid token, expected: a lowercase alphanumeric (including
        underscore) string starting with a letter

The problem here is that the error doesn't help us understand why pub doesn't work. It would be good to write what we got instead.

Perhaps this can be done everywhere by also including the obtained token in the error? So something like this:

_ => Err(ctx.error(
                ErrorKind::ExpectedToken(TokenKind::Identifier("".to_string())),
                token.span,
            )),

could become

_ => Err(ctx.error(
                ErrorKind::ExpectedToken(TokenKind::Identifier("".to_string()), TokenKind::Keyword(...)),
                token.span,
            )),

for example

[Lynette7]

Hello, I would love to contribute to this issue.

[zedar]

Hello, please find my PR for this issue. @Lynette7 maybe you can base on my PR.