chore(demo): add examples to demo app (#10743)

* chore(demo): add examples to demo app

* fix polyfill

Author: andrewseguin

.github/CODEOWNERS

@@ -109,6 +109,8 @@
 /src/demo-app/demo-app/**                          @jelbourn
 /src/demo-app/dialog/**                            @jelbourn @crisbeto
 /src/demo-app/drawer/**                            @mmalerba
+/src/demo-app/example/**                           @andrewseguin
+/src/demo-app/examples-page/**                     @andrewseguin
 /src/demo-app/expansion/**                         @josephperrott
 /src/demo-app/focus-origin/**                      @mmalerba
 /src/demo-app/gestures/**                          @jelbourn