feat(links)!: allow granular highlighting of links

[kristijanhusak]

Summary

Previously, both link with and without description were highlighted only with @org.hyperlink hl group, which was linked to @markup.link.url by default.
Since Neovim also has @markup.link and @markup.link.label in addition to @markup.link.url, use those hl groups accordingly.

1. @org.hyperlink for the non-important parts of link (square brackets), and this hl group is now linked to @markup.link
2. @org.hyperlink.url for the actual url in the link. Hl group linked to @markup.link.url by default
3. @org.hyperlink.desc for the link description. Hl group linked to @markup.link.label by default

To return to the previous behavior, override @org.hyperlink.url and @org.hyperlink.desc as suggested in the docs:

vim.api.nvim_create_autocmd('ColorScheme', {
  pattern = '*',
  callback = function()
    vim.api.nvim_set_hl(0, '@org.hyperlink', { link = '@markup.link.url' })
    vim.api.nvim_set_hl(0, '@org.hyperlink.url', { link = '@org.hyperlink' })
    vim.api.nvim_set_hl(0, '@org.hyperlink.desc', { link = '@org.hyperlink' })
  end
})

Related Issues

Closes #961

Checklist

I confirm that I have:

• Followed the
  Conventional Commits
  specification (e.g., feat: add new feature, fix: correct bug,
  docs: update documentation).
• My PR title also follows the conventional commits specification.
• Updated relevant documentation, if necessary.
• Thoroughly tested my changes.
• Added tests (if applicable) and verified existing tests pass with
  make test.
• Checked for breaking changes and documented them, if any.