Improve import error suggestions

[sobolevn]

This is the first PR in the series.

This case is not covered yet:

#[test]
fn import_submodule_as_value() {
    assert_with_module_error!(
        ("one/two", "pub fn whatever() {}"),
        "
        import one.{two}
        "
    );
}

It requires a bit tricky logic to get right, so I decided to split it out.

Better wordings are more than welcome! 👍

[sobolevn]

Ok, I failed to make suggestions shorter 🙈 They are now longer.

Changes:

1. I modified how did_you_mean suggestions are applied, because we can literally have this use-case:

#[test]
fn import_value_as_submodule3() {
    // Two possible suggestions: `import one/wobble` or `import one.{wibble}`
    // One via hint, one via `did_you_mean`.
    assert_with_module_error!(
        ("one", "pub fn wibble() {}"),
        ("one/wobble", ""),
        "import one/wibble"
    );
}

We should suggest both:

• import one/wobble
• import one.{wibble}

Because it is not clear what was meant. Now we do both suggestions.

• I changed imported_modules to importable_modules, because imported_modules were always empty in analyze, so we can have better suggestions.
• I provided a link to the docs, since this topic is rather complex.

Sadly, we cannot apply suggestions from #3553 (comment) which are great, because of syntax error limitations :(
Ideally there should be no syntax error here and all errors should come from analyze step, but it is a very complex and probably-not-justified change.

Please, take a look!

[lpil]

I'm finding it confusing the way that 2 different suggestions are presenting in 2 different ways now. I think it should only present 1 suggestion and it should always be presented in the same way.

[lpil]

gleam isn't a package, this would be to import the module gleam/io

[lpil]

Merge this into the existing unknown module error please

[lpil]

What are name parts?

[lpil]

This isn't the correct formatting. Wrapping shouldn't be applied to code.

[lpil]

Hello! Are you still working on this one? Thanks

[sobolevn]

Sorry, no :(
I got busy on my work projects. Feel free to close / transfer to someone else.