chore(doc-gen): render @example tag for ngdoc @method

Currently, ngdoc @method ignores @example tags. Examples are usually
rendered directly into the @description via code blocks or <example>
elements. However, some methods still have @example tags (possibly
from a previous docs version), which are currently not visible.

While not absolutely necessary, having special markup for Examples
makes them a) easier to find visually in the docs, and b) easier
to link to as they will have a unique id.

Closes #14722

Author: Narretz

docs/config/templates/ngdoc/api/api.template.html

@@ -51,7 +51,7 @@ <h2 id="dependencies">Dependencies</h2>
 
   {% block examples %}
   {%- if doc.examples %}
-  <h2 id="example">Example</h2>
+  <h2 id="example">Examples</h2>
   {%- for example in doc.examples -%}
     {$ example | marked $}
   {%- endfor -%}

docs/config/templates/ngdoc/lib/methods.template.html

@@ -26,6 +26,13 @@ <h4>Returns</h4>
     {$ lib.typeInfo(method.returns) $}
     {% endif %}
 
+    {%- if method.examples %}
+    <h4 id="{$ doc.name $}.{$ method.name $}-examples">Examples</h4>
+    {%- for example in method.examples -%}
+      {$ example | marked $}
+    {%- endfor -%}
+    {% endif -%}
+
   </li>
   {% endfor -%}
 </ul>