fixes #19396; Nimdoc hide nonexported fields (#21305)

* suppresses non-exported fields of types and adds command-line option to re-enable this if desired

* corrected the doctest that produced a CI error

* an embarrassingly bad error in reasoning

* modified a nimdoc test to reflect updated behavior

* needed another change to bring utils.html doctest in sync with update

* add info

* fix nimdoc

* lint

* render postfix

* fixes a problem

* fixes nimdoc

* fix nimdoc

---------

Co-authored-by: johnperry-math <john.perry@usm.edu>
Co-authored-by: johnperry-math <devotus@yahoo.com>

nimdoc/extlinks/project/expected/main.html

@@ -55,8 +55,7 @@
   <details open>
     <summary><a class="reference reference-toplevel" href="#7" id="57">Types</a></summary>
     <ul class="simple simple-toc-section">
-      <li><a class="reference" href="#A" title="A = object
-  x: int">A</a></li>
+      <li><a class="reference" href="#A" title="A = object">A</a></li>
 
     </ul>
   </details>
@@ -97,8 +96,7 @@
   <dl class="item">
     <div id="A">
   <dt><pre><a href="main.html#A"><span class="Identifier">A</span></a> <span class="Other">=</span> <span class="Keyword">object</span>
-  <span class="Identifier">x</span><span class="Other">:</span> <span class="Identifier">int</span>
-</pre></dt>
+  </pre></dt>
   <dd>