doc anchor doesn't work for strings which need to encode in URL

[stzn]

Description

I use Japanese to headings like "## テスト" in a markdown, and I'd like to use it for an anchor like "doc:SomeMarkdown:テスト". But it doesn't work.

If I change "テスト" to "test" ( "doc:SomeMarkdown:test"), it works well.

Related forums thread: https://forums.swift.org/t/can-docc-auto-generate-anchors-be-used-in-non-ascii-strings/62295

Checklist

• If possible, I've reproduced the issue using the main branch of this package.
• This issue hasn't been addressed in an existing GitHub issue.

Expected Behavior

Strings which need to encode in URL for a heading can be used as an anchor.

Actual behavior

URL does encoding of the fragment identifier, but there is no encoding done in the id attribute of the HTML for the heading.

For example,

I confirmed it in swift-book repository.

Steps To Reproduce

1. Use strings which need to encode in URL for a heading in a markdown
2. Use it as an anchor.

Swift-DocC Version Information

main branch

Swift Compiler Version Information

swift-driver version: 1.62.15 Apple Swift version 5.7.1 (swiftlang-5.7.1.135.3 clang-1400.0.29.51)
Target: x86_64-apple-macosx13.0

[stzn]

As far as I confirmed, the difference between cmark-gfm and swift-docc probably causes this issue.

When creating the value of the href in cmark-gfm, it escapes characters except "-_.+!*'(),%#@?=;:/,+&$~ alphanum". So "テスト" was escaped.
https://github.com/github/cmark-gfm/blob/6a6e335709ef68cf2c616eeaf61b09ed4c654669/src/houdini_href_e.c#L46

But, according to RFC3986, Japanese are allowed, so URLComponents(string:) can be instantiated and "テスト"　　is outputted as it is. That's why a valid ValidatedURL could be returned here.
https://github.com/apple/swift-docc/blob/f11ea837fb1db953b98707c01ab671ccc0d38dbf/Sources/SwiftDocC/Utility/ValidatedURL.swift#L60