🐛 FIX: Double encoded ampersands in query params

[sumezulike]

This closes #760.

MyST already escapes the & in the query params, but docutils escapes them again when rendering HTML, leading to broken query params.

[Link](example.com?foo=1&bar=2)

becomes

<p><a href="example.com?foo=1&amp;amp;bar=2">Link</a></p>

instead of

<p><a href="example.com?foo=1&amp;bar=2">Link</a></p>

These changes to the docutils parser override the HTMLTranslator.encode function so already encoded ampersands are not encoded again.
Since the issue lies in the interaction with docutils, I think it makes sense to fix it here.
Also, simply removing the escapeHtml call in MyST makes the sphinx app doctree XML files invalid because the ampersands aren't escaped.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.15%. Comparing base (3d84ff8) to head (1151bee).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #929      +/-   ##
==========================================
+ Coverage   90.13%   90.15%   +0.02%     
==========================================
  Files          24       24              
  Lines        3416     3423       +7     
==========================================
+ Hits         3079     3086       +7     
  Misses        337      337              

Flag	Coverage Δ
pytests	90.15% <100.00%> (+0.02%)	⬆️

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[chrisjsewell]

I'm afraid this is not something that cannot be merged; it would break restructuredtext parsing.

Monkey patching is done strictly as a last resort, and only for where the patch does not affect upstream use