Move add collection pane to React (#486)

* Move add collection pane to React

* Add feature flag

* fix unit tests

* FIx merge conflicts and address comments

* Resolve merge conflicts

* Address comments

* Fix e2e test failure

* Update test snapshots

* Update test snapshots

src/Explorer/Controls/CollapsiblePanel/CollapsibleSectionComponent.test.tsx

@@ -6,6 +6,7 @@ describe("CollapsibleSectionComponent", () => {
   it("renders", () => {
     const props: CollapsibleSectionProps = {
       title: "Sample title",
+      isExpandedByDefault: true,
     };
 
     const wrapper = shallow(<CollapsibleSectionComponent {...props} />);