doc/go1.19: add TODOs for changes to go/types

Add TODO items for significant changes to go/types: the inclusion of
Origin methods for Var and Func, and a re-working of Named types to
ensure finiteness of reachable types via their API.

Updates #51400

Change-Id: I0f2a972023a5d5f995de3c33e9e2b0a4213e900a
Reviewed-on: https://go-review.googlesource.com/c/go/+/410614
Reviewed-by: Robert Griesemer <gri@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

doc/go1.19.html

@@ -268,6 +268,17 @@ <h3 id="minor_library_changes">Minor changes to the library</h3>
   </dd>
 </dl><!-- go/parser -->
 
+<dl id="go/types"><dt><a href="/pkg/go/types/">go/types</a></dt>
+  <dd>
+    <p><!-- CL 395535 -->
+      TODO: <a href="https://go.dev/cl/395535">https://go.dev/cl/395535</a>: add Var.Origin and Func.Origin
+    </p>
+    <p><!-- CL 404885 -->
+      TODO: <a href="https://go.dev/cl/404885">https://go.dev/cl/404885</a>: a finite number of types are reachable via Named.Underlying, Named.Method
+    </p>
+  </dd>
+</dl><!-- go/types -->
+
 <dl id="image/draw"><dt><a href="/pkg/image/draw/">image/draw</a></dt>
   <dd>
     <p><!-- CL 396795 -->