build(docs-infra): render all overloads if they are abstract (#25670)

In an overloaded method, the overload with the function body is the
actual method doc, and this doc is not included in the list of "additional"
overloads.

Moreover, the logic (all in dgeni-packages) is that if none of the items
has a body then we use the first overload as the actual method doc.

In the case of abstract methods, none of the methods have a body. So we
have a situation where the overloads collection does not contain the first
abstract method, even though it is not the "implementation" of the method.
Therefore we need to still render it.

Closes #25610

PR Close #25670

aio/tools/transforms/templates/api/lib/memberHelpers.html

@@ -47,6 +47,11 @@
 
 <code-example language="ts" hideCopy="true" linenums="false" class="no-box api-heading">{$ renderMemberSyntax(overload) $}</code-example>
 
+{% if overload.deprecated !== undefined %}
+<div class="deprecated">
+  {$ ('**Deprecated** ' + overload.deprecated) | marked $}
+</div>{% endif %}
+
 <h4 class="no-anchor">Parameters</h4>
 {$ params.renderParameters(overload.parameterDocs, cssClass + '-parameters', cssClass + '-parameter') $}
 
@@ -97,6 +102,13 @@
       </td>
     </tr>
   {% elseif method.overloads.length < 3 -%}
+    {% if method.isAbstract %}
+      <tr>
+        <td>
+          {$ renderOverloadInfo(method, cssClass + '-overload', method) $}
+        </td>
+      </tr>
+    {% endif %}
     {% for overload in method.overloads -%}
     <tr>
       <td>
@@ -110,7 +122,11 @@
         <details class="overloads">
           <summary><h4 class="no-anchor">{$ method.overloads.length $} overloads...</h4></summary>
           <div class="detail-contents">
-              {% for overload in method.overloads %}
+                {% if method.isAbstract %}
+                  {$ renderOverloadInfo(method, cssClass + '-overload', method) $}
+                  <hr class="hr-margin fullwidth">
+                {% endif %}
+                {% for overload in method.overloads %}
                 {$ renderOverloadInfo(overload, cssClass + '-overload', method) $}
                 {% if not loop.last %}<hr class="hr-margin fullwidth">{% endif %}
               {% endfor %}