feature request: check text fragments

Text fragments are a standardized way to link to webpage text without relying on HTML ID attributes. They are supported by all modern browsers. I'd like to use lychee to make sure my text fragment links are valid!

Example:

<!-- file.html -->
<html>
  <body>
    <div>
      <a href="https://developer.mozilla.org/en-US/docs/Web/URI/Fragment/Text_fragments#:~:text=without%20relying%20on%20the%20presence%20of%20IDs">
        valid
      </a>
      <a href="https://developer.mozilla.org/en-US/docs/Web/URI/Fragment/Text_fragments#:~:text=asdfawefaweafa">
        invalid
      </a>
    </div>
  </body>
</html>

; lychee --version
# lychee 0.16.1
; lychee -vv --include-fragments ./file.html
#     [200] https://developer.mozilla.org/en-US/docs/Web/URI/Fragment/Text_fragments#:~:text=without%20relying%20on%20the%20presence%20of%20IDs
#     [200] https://developer.mozilla.org/en-US/docs/Web/URI/Fragment/Text_fragments#:~:text=asdfawefaweafa

Desired behavior: if lychee is configured to check fragments and is passed a #:~:text=... fragment, lychee should throw an error if the text is not found within the linked document.

lycheeverse / lychee

feature request: check text fragments #1545