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

Currently, ngdoc `@method` ignores `@example` tags and does not output them.
This is usually not a problem, as examples are mostly defined directly
in the `@description` via code blocks or `<example>`
elements. However, some methods still have `@example` tags (possibly
from a previous docs version).

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
Closes #15448

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

@@ -51,7 +51,7 @@
 
   {% 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 @@
     {$ 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>