Replace Toolbar showHistory group with individual showRedo and showUndo (#603)

lib/src/widgets/toolbar.dart

@@ -94,7 +94,8 @@ class QuillToolbar extends StatelessWidget implements PreferredSizeWidget {
     bool showQuote = true,
     bool showIndent = true,
     bool showLink = true,
-    bool showHistory = true,
+    bool showUndo = true,
+    bool showRedo = true,
     bool multiRowsDisplay = true,
     bool showImageButton = true,
     bool showVideoButton = true,
@@ -124,7 +125,6 @@ class QuillToolbar extends StatelessWidget implements PreferredSizeWidget {
     Key? key,
   }) {
     final isButtonGroupShown = [
-      showHistory ||
           showBoldButton ||
           showItalicButton ||
           showSmallButton ||
@@ -155,7 +155,7 @@ class QuillToolbar extends StatelessWidget implements PreferredSizeWidget {
       multiRowsDisplay: multiRowsDisplay,
       locale: locale,
       children: [
-        if (showHistory)
+        if (showUndo)
           HistoryButton(
             icon: Icons.undo_outlined,
             iconSize: toolbarIconSize,
@@ -163,7 +163,7 @@ class QuillToolbar extends StatelessWidget implements PreferredSizeWidget {
             undo: true,
             iconTheme: iconTheme,
           ),
-        if (showHistory)
+        if (showRedo)
           HistoryButton(
             icon: Icons.redo_outlined,
             iconSize: toolbarIconSize,