[improvement] TreeSelect: support disable option (#2107)

packages/tree-select/test/__snapshots__/demo.spec.js.snap

@@ -26,7 +26,7 @@ exports[`renders demo correctly 1`] = `
           温州
           <!---->
         </div>
-        <div class="van-ellipsis van-tree-select__item">
+        <div class="van-ellipsis van-tree-select__item van-tree-select__item--disabled">
           宁波
           <!---->
         </div>

packages/tree-select/test/index.spec.js

@@ -14,11 +14,17 @@ test('select item', () => {
     propsData: {
       items: [{
         text: 'group1',
-        children: [item]
+        children: [
+          item,
+          { ...item, disabled: true }
+        ]
       }]
     }
   });
 
-  wrapper.find('.van-tree-select__item').trigger('click');
+  const items = wrapper.findAll('.van-tree-select__item');
+  items.at(0).trigger('click');
   expect(wrapper.emitted('itemclick')[0][0]).toEqual(item);
+  items.at(1).trigger('click');
+  expect(wrapper.emitted('itemclick')[1]).toBeFalsy();
 });