Attach, show and hide pane item views with native DOM APIs

We continue to invoke SpacePen attach hooks on any shim wrappers
for backward compatibility, but SpacePen wrappers are no longer required
for attoch/hide/show as they were previously. Next: removal.

src/pane-element.coffee

@@ -1,5 +1,5 @@
 {CompositeDisposable} = require 'event-kit'
-{$} = require './space-pen-extensions'
+{$, callAttachHooks, callRemoveHooks} = require './space-pen-extensions'
 PaneView = require './pane-view'
 
 class PaneElement extends HTMLElement
@@ -8,6 +8,8 @@ class PaneElement extends HTMLElement
   createdCallback: ->
     @attached = false
     @subscriptions = new CompositeDisposable
+    @inlineDisplayStyles = new WeakMap
+
     @initializeContent()
     @subscribeToDOMEvents()
     @createSpacePenShim()
@@ -81,12 +83,32 @@ class PaneElement extends HTMLElement
   activeItemChanged: (item) ->
     return unless item?
 
-    $itemViews = $(@itemViews)
-    view = @model.getView(item).__spacePenView
-    otherView.hide() for otherView in $itemViews.children().not(view).views()
-    $itemViews.append(view) unless view.parent().is($itemViews)
-    view.show() if @attached
-    view.focus() if @hasFocus()
+    hasFocus = @hasFocus()
+    itemView = @model.getView(item)
+
+    for child in @itemViews.children
+      if child is itemView
+        @showItemView(child) if @attached
+      else
+        @hideItemView(child)
+
+    unless @itemViews.contains(itemView)
+      @itemViews.appendChild(itemView)
+      callAttachHooks(itemView)
+
+    itemView.focus() if hasFocus
+
+  showItemView: (itemView) ->
+    inlineDisplayStyle = @inlineDisplayStyles.get(itemView)
+    if inlineDisplayStyle?
+      itemView.style.display = inlineDisplayStyle
+    else
+      itemView.style.display = ''
+
+  hideItemView: (itemView) ->
+    inlineDisplayStyle = itemView.style.display
+    @inlineDisplayStyles.set(itemView, inlineDisplayStyle) if inlineDisplayStyle?
+    itemView.style.display = 'none'
 
   itemRemoved: ({item, index, destroyed}) ->
     if item instanceof $