Make type defs for lexical react (#1369)

* Add Flow type definitions for Lexical React

* Fix bugs

* Revert bad merge

packages/lexical-react/flow/LexicalHorizontalRuleNode.js.flow

@@ -0,0 +1,25 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ * @flow strict
+ */
+
+import type {LexicalNode} from 'lexical';
+
+import {DecoratorNode} from 'lexical';
+
+declare export class HorizontalRuleNode extends DecoratorNode<React$Node> {
+  static getType(): string;
+  static clone(node: HorizontalRuleNode): HorizontalRuleNode;
+  createDOM(): HTMLElement;
+  getTextContent(): '\n';
+  isTopLevel(): true;
+  updateDOM(): false;
+  decorate(): React$Node;
+}
+
+declare export function $createHorizontalRuleNode(): HorizontalRuleNode;
+declare export function $isHorizontalRuleNode(node: ?LexicalNode): boolean;