build(aio): move doc-gen stuff from angular.io (#14097)

docs/templates/lib/paramList.html

@@ -0,0 +1,12 @@
+{% macro paramList(params) -%}
+  {%- if params -%}
+    ({%- for param in params -%}
+      {$ param | escape $}{% if not loop.last %}, {% endif %}
+    {%- endfor %})
+  {%- endif %}
+{%- endmacro -%}
+
+
+{% macro returnType(returnType) -%}
+  {%- if returnType %} : {$ returnType | escape $}{% endif -%}
+{%- endmacro -%}