Settings WebUI: move cursor pointer style to label

When a div has its cursor style set to pointer, it is highlighted when
clicked. This can be replicated on desktop using the dev tools device
toolbar. When expand button does not have a label, the expand button
is highlighted. The actionable attribute is used set the cursor style
to pointer. The label div has has 0 dimensions when no label is slotted.
Moving the actionable attribute down to the label div works for both
when a label is present and missing.

Bug: 907057
Change-Id: I23a0950b789c842739997554a3232c1805b3089e
Reviewed-on: https://chromium-review.googlesource.com/c/1344819Reviewed-by: Scott Chen <scottchen@chromium.org>
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610170}

ui/webui/resources/cr_elements/cr_expand_button/cr_expand_button.html

@@ -25,8 +25,8 @@
         flex: 1;
       }
     </style>
-    <div id="outer" actionable>
-      <div id="label"><slot></slot></div>
+    <div id="outer">
+      <div id="label" actionable><slot></slot></div>
       <paper-icon-button-light class$="[[iconName_(expanded)]]">
         <button disabled="[[disabled]]" aria-label$="[[alt]]"
             aria-pressed$="[[getAriaPressed_(expanded)]]"