feat(Overlay): add default slot (#4571)

src/overlay/test/__snapshots__/index.spec.js.snap

@@ -2,6 +2,8 @@
 
 exports[`class-name prop 1`] = `<div class="van-overlay my-overlay" style="z-index: 1;" name="van-fade"></div>`;
 
+exports[`default slot 1`] = `<div class="van-overlay" style="z-index: 1; display: none;" name="van-fade">Custom Default</div>`;
+
 exports[`duration prop 1`] = `<div class="van-overlay" style="z-index: 1; animation-duration: 1s;" name="van-fade"></div>`;
 
 exports[`z-index prop 1`] = `<div class="van-overlay" style="z-index: 99;" name="van-fade"></div>`;

src/overlay/test/index.spec.js

@@ -47,3 +47,13 @@ test('click event', () => {
   wrapper.trigger('click');
   expect(onClick).toHaveBeenCalledTimes(1);
 });
+
+test('default slot', () => {
+  const wrapper = mount(Overlay, {
+    scopedSlots: {
+      default: () => 'Custom Default'
+    }
+  });
+
+  expect(wrapper).toMatchSnapshot();
+});