Multiple Reference Calls to the Same Footnote

[String10]

Describe the bug
Multiple reference call to the same footnotes will only generate one footnote-to-content link.

To Reproduce
Check the following markdown:

Several calls[^1] [^1] to the same definition may occur.

[^1]: One definition here.

Then we get:

<p>Several calls<sup id="fnref-1"><a href="#fn-1" class="footnote-ref">1</a></sup> <sup id="fnref-1"><a href="#fn-1" class="footnote-ref">1</a></sup> to the same definition may occur.</p>
<div class="footnotes">
  <hr>
  <ol>
    <li id="fn-1">One definition here.<a href="#fnref-1" class="footnote-backref">↩</a></li>
  </ol>
</div>

Two reference calls get the same id and click the back link will only lead to the first call.

Expected behavior

Something like this:

<p>Several calls<sup id="fnref-1"><a href="#fn-1" class="footnote-ref">1</a></sup> <sup id="fnref-1:1"><a href="#fn-1" class="footnote-ref">1</a></sup> to the same definition may occur.</p>
<div class="footnotes">
  <hr>
  <ol>
    <li id="fn-1">One definition here.<a href="#fnref-1" class="footnote-backref">↩</a><a href="#fnref-1-1" class="footnote-backref">↩</a></li>
  </ol>
</div>

Additional context
See String10/KGarden#37 for more details.