relicense appflowy editor (#1938)

* revert:"fix: remove keyword when click selection menu item"

This reverts commit 5782dec45c.

* revert(appflowy_editor):revert "feat: double asterisks/underscores to bold text"

This reverts commit c0964fad5d.

* revert(appflowy_editor):revert "fix: workaround infinity formatting"

This reverts commit 6a902a2b21.
The Appflowy folder under the frontend had been removed before reverting.

* chore(appflow_editor):update test variable after reverting

* chore(appflowy_editor): comment out the test for reverting

* chore(appflowy_editor): update variable type after reverting

* chore(appflowy_editor): remove unused import after reverting

* feat(appflowy_editor): double asterisk to bold text

* test(appflowy_editor): test double asterisk to bold text

* fix(appflowy_editor): delete slash after a selection menu item is selected

* test(appflowy_editor): test selection menu widget after clicking

* feat(appflowy_editor):  double asterisk to bold text and remove slash after clicking selection menu item   (#1935)

* feat(appflowy_editor): double asterisk to bold text

* test(appflowy_editor): test double asterisk to bold text

* fix(appflowy_editor): delete slash after a selection menu item is selected

* test(appflowy_editor): test selection menu widget after clicking

* feat(appflowy_editor): double underscore to bold text

* test(appflowy_editor): test double underscore to bold text

* chore(appflowy_editor): put checkbox testing back

* chore: format code

---------

Co-authored-by: Yijing Huang <hyj891204@gmail.com>

frontend/appflowy_flutter/lib/plugins/document/presentation/plugins/board/board_menu_item.dart

@@ -7,7 +7,7 @@ import 'package:flowy_infra/image.dart';
 import 'package:flutter/material.dart';
 
 SelectionMenuItem boardMenuItem = SelectionMenuItem(
-  name: () => LocaleKeys.document_plugins_referencedBoard.tr(),
+  name: LocaleKeys.document_plugins_referencedBoard.tr(),
   icon: (editorState, onSelected) {
     return svgWidget(
       'editor/board',

frontend/appflowy_flutter/lib/plugins/document/presentation/plugins/grid/grid_menu_item.dart

@@ -7,7 +7,7 @@ import 'package:flowy_infra/image.dart';
 import 'package:flutter/material.dart';
 
 SelectionMenuItem gridMenuItem = SelectionMenuItem(
-  name: () => LocaleKeys.document_plugins_referencedGrid.tr(),
+  name: LocaleKeys.document_plugins_referencedGrid.tr(),
   icon: (editorState, onSelected) {
     return svgWidget(
       'editor/grid',

frontend/appflowy_flutter/lib/plugins/document/presentation/plugins/horizontal_rule_node_widget.dart

@@ -37,7 +37,7 @@ ShortcutEventHandler _insertHorzaontalRule = (editorState, event) {
 };
 
 SelectionMenuItem horizontalRuleMenuItem = SelectionMenuItem(
-  name: () => 'Horizontal rule',
+  name: 'Horizontal rule',
   icon: (editorState, onSelected) => Icon(
     Icons.horizontal_rule,
     color: onSelected