PAINTROID-454: Flutter: Add Layers

lib/core/providers/state/layers_panel_visibility_state_provider.dart

@@ -0,0 +1,24 @@
+import 'package:riverpod_annotation/riverpod_annotation.dart';
+
+part 'layers_panel_visibility_state_provider.g.dart';
+
+@riverpod
+class LayersPanelVisibilityStateProvider
+    extends _$LayersPanelVisibilityStateProvider {
+  void toggleVisibility() {
+    state = !state;
+  }
+
+  void show() {
+    state = true;
+  }
+
+  void hide() {
+    state = false;
+  }
+
+  @override
+  bool build() {
+    return false;
+  }
+}

lib/ui/pages/workspace_page/components/bottom_bar/bottom_nav_bar.dart

@@ -1,10 +1,9 @@
+import 'package:colorpicker/colorpicker.dart';
 import 'package:flutter/material.dart';
-
 import 'package:flutter_riverpod/flutter_riverpod.dart';
-import 'package:colorpicker/colorpicker.dart';
-
 import 'package:paintroid/core/enums/tool_types.dart';
 import 'package:paintroid/core/localization/app_localizations.dart';
+import 'package:paintroid/core/providers/state/layers_panel_visibility_state_provider.dart';
 import 'package:paintroid/core/providers/state/paint_provider.dart';
 import 'package:paintroid/core/providers/state/tool_options_visibility_state_provider.dart';
 import 'package:paintroid/core/providers/state/toolbox_state_provider.dart';
@@ -92,6 +91,9 @@ void _onNavigationItemSelected(int index, BuildContext context, WidgetRef ref) {
     case BottomNavBarItem.COLOR:
       _showColorPicker(context, ref);
       break;
+    case BottomNavBarItem.LAYERS:
+      _handleLayersPanelVisibility(ref);
+      break;
     default:
       return;
   }
@@ -112,6 +114,10 @@ void _handleToolOptionsVisibility(WidgetRef ref) {
   ref.read(toolOptionsVisibilityStateProvider.notifier).toggleVisibility();
 }
 
+void _handleLayersPanelVisibility(WidgetRef ref) {
+  ref.read(layersPanelVisibilityStateProvider.notifier).toggleVisibility();
+}
+
 void _showColorPicker(BuildContext context, WidgetRef ref) {
   final Color initialColor = ref.read(paintProvider).color;