Add Menu component (#3097)

* Add POC menu abstraction

* Better platform handling

* Remove ignore

* Add some menu items

* Add controlled dropdown

* Pass through a11y props

* Ignore uninitialized context

* Tweaks

* Usability improvements

* Rename handlers to props

* Add radix comment

* Ignore known type

* Remove todo

* Move storybook item

* Improve Group matching

* Adjust theming

bskyweb/templates/base.html

@@ -213,6 +213,7 @@
     }
 
     /* NativeDropdown component */
+    .radix-dropdown-item:focus,
     .nativeDropdown-item:focus {
       outline: none;
     }