Override jQuery.contains instead of jQuery.fn.position

Turns out the problems with position inside the shadow DOM are due to
the fact that elements in the light DOM don’t claim to contain elements
from a shadow DOM, causing jQuery.fn.offset to bail out early and
misreport positions inside the editor.

src/space-pen-extensions.coffee

@@ -78,10 +78,17 @@ jQuery.event.remove = (elem, types, originalHandler, selector, mappedTypes) ->
     handler = HandlersByOriginalHandler.get(originalHandler) ? originalHandler
   JQueryEventRemove(elem, types, handler, selector, mappedTypes, RemoveEventListener if atom?.commands?)
 
-jQuery.fn.position = ->
-  top = @[0].offsetTop
-  left = @[0].offsetLeft
-  {top, left}
+JQueryContains = jQuery.contains
+
+jQuery.contains = (a, b) ->
+  shadowRoot = null
+  currentNode = b
+  while currentNode
+    if currentNode instanceof ShadowRoot and a.contains(currentNode.host)
+      return true
+    currentNode = currentNode.parentNode
+
+  JQueryContains.call(this, a, b)
 
 tooltipDefaults =
   delay: