fix(console): print <br /> when having a newline

[ematipico]

Summary

The HTML emitted by our adapter was causing a parsing error when used inside MDX files.

It turns out that MDX doesn't like \n\n inside HTML. I think it's a reasonable parsing error.

This PR fixes the issue by changing \n to a <br />. While <br> should be accepted, MDX doesn't like it, so it's safer to use <br /> instead.

This PR changes the existing adapter and renames it. Unfortunately, I tried to use a new adapter but that required more work, so I decided to update the existing one.

Test Plan

I added new tests to avoid possible regressions. Once merged, I will send a PR to the website to fix everything.

[ematipico]

I am going to merge this, since I need this fix in the website repository. Let me know if there are any concerns, I will follow up

[chansuke]

I've read the code and I believe adding some test cases would be beneficial

1. adding tests for more escape characters, such as '&', '<', and '>':

2. testing multiple new lines like below

#[test]
fn test_multiple_newlines() {
    let mut buf = Vec::new();
    let mut writer = super::HTML(&mut buf);
    let mut formatter = Formatter::new(&mut writer);
    formatter
        .write_markup(markup! {
            "Line1\nLine2\rLine3\n\rLine4"
        })
        .unwrap();
    assert_eq!(String::from_utf8(buf).unwrap(), "Line1<br />Line2<br />Line3<br /><br />Line4");
}

@ematipico
If this approach looks good to you, I’d be happy to submit a PR.