Add deprecation warning while importing Slider component (#23385)

Summary:
Introducing the deprecation warning for those who are importing `Slider` component (#23313)

[General] [Deprecated] - Deprecated Slider as it has now been moved to `react-native-community/slider`
Pull Request resolved: #23385

Differential Revision: D14029819

Pulled By: cpojer

fbshipit-source-id: 7ad257124756c6bee57c3fbb1a056c09e8cc29a1

Libraries/react-native/react-native-implementation.js

@@ -104,6 +104,12 @@ module.exports = {
     return require('SegmentedControlIOS');
   },
   get Slider() {
+    warnOnce(
+      'slider-moved',
+      'Slider has been extracted from react-native core and will be removed in a future release. ' +
+        "It can now be installed and imported from '@react-native-community/slider' instead of 'react-native'. " +
+        'See https://github.com/react-native-community/react-native-slider',
+    );
     return require('Slider');
   },
   get SnapshotViewIOS() {