Feat: Move FlatLists to @react-native/flat-lists package

Summary: This diff moves `FlatList` and `SectionList` to a new package `@react-native/flat-lists`.
This is a first step towards moving all the `FlatList`-related code to a separate package.
This will allow us to make changes to the `FlatList` implementation without affecting the rest of the React Native codebase.

Changelog: [General] [Changed] - Move `FlatList`s to `@react-native/flat-lists` package.
`FlatList` and `SectionList` are now available in `@react-native/flat-lists` package.
**Warning**: This is a breaking(?) change, and you will need to update your imports to use the new package.

Libraries/Animated/components/AnimatedFlatList.js

@@ -10,8 +10,8 @@
 
 import type {AnimatedComponentType} from '../createAnimatedComponent';
 
-import FlatList from '../../Lists/FlatList';
 import createAnimatedComponent from '../createAnimatedComponent';
+import FlatList from '@react-native/flat-lists/Lists/FlatList';
 import * as React from 'react';
 
 /**

Libraries/Animated/components/AnimatedSectionList.js

@@ -10,8 +10,8 @@
 
 import type {AnimatedComponentType} from '../createAnimatedComponent';
 
-import SectionList from '../../Lists/SectionList';
 import createAnimatedComponent from '../createAnimatedComponent';
+import SectionList from '@react-native/flat-lists/Lists/SectionList';
 import * as React from 'react';
 
 /**

Libraries/Inspector/NetworkOverlay.js

@@ -15,11 +15,11 @@ import type {RenderItemProps} from '../Lists/VirtualizedList';
 const ScrollView = require('../Components/ScrollView/ScrollView');
 const TouchableHighlight = require('../Components/Touchable/TouchableHighlight');
 const View = require('../Components/View/View');
-const FlatList = require('../Lists/FlatList');
 const XHRInterceptor = require('../Network/XHRInterceptor');
 const StyleSheet = require('../StyleSheet/StyleSheet');
 const Text = require('../Text/Text');
 const WebSocketInterceptor = require('../WebSocket/WebSocketInterceptor');
+const FlatList = require('@react-native/flat-lists/Lists/FlatList');
 const React = require('react');
 
 const LISTVIEW_CELL_HEIGHT = 15;