Convert ScrollViewStickyHeader to functional component and gate the change

Summary:
Changelog:
[Internal][Added] - Use injected ScrollViewStickyHeader if set

Reviewed By: lunaleaps

Differential Revision: D26931404

fbshipit-source-id: 6f6f1b501b610a05999898be3e2ce08aeb4dab1b

Libraries/Components/ScrollView/ScrollViewStickyHeader.js

@@ -20,6 +20,8 @@ import Platform from '../../Utilities/Platform';
 
 import type {LayoutEvent} from '../../Types/CoreEventTypes';
 
+import ScrollViewStickyHeaderInjection from './ScrollViewStickyHeaderInjection';
+
 const AnimatedView = AnimatedImplementation.createAnimatedComponent(View);
 
 export type Props = $ReadOnly<{
@@ -328,4 +330,8 @@ const styles = StyleSheet.create({
   },
 });
 
-module.exports = ScrollViewStickyHeader;
+const SHToExport: React.AbstractComponent<
+  Props,
+  $ReadOnly<{setNextHeaderY: number => void, ...}>,
+> = ScrollViewStickyHeaderInjection.unstable_SH ?? ScrollViewStickyHeader;
+module.exports = SHToExport;

Libraries/Components/ScrollView/ScrollViewStickyHeaderInjection.js

@@ -0,0 +1,17 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @format
+ * @flow
+ */
+
+'use strict';
+
+import typeof ScrollViewStickyHeader from './ScrollViewStickyHeader';
+
+export default {
+  unstable_SH: (null: ?ScrollViewStickyHeader),
+};