add 'Long press to zoom' setting

lib/foundation/appdata.dart

@@ -111,6 +111,7 @@ class _Settings with ChangeNotifier {
     'language': 'system', // system, zh-CN, zh-TW, en-US
     'cacheSize': 2048, // in MB
     'downloadThreads': 5,
+    'enableLongPressToZoom': true,
   };
 
   operator [](String key) {

lib/pages/reader/images.dart

@@ -223,6 +223,9 @@ class _GalleryModeState extends State<_GalleryMode>
 
   @override
   void handleLongPressDown(Offset location) {
+    if(!appdata.settings['enableLongPressToZoom']) {
+      return;
+    }
     var photoViewController = photoViewControllers[reader.page]!;
     double target = photoViewController.getInitialScale!.call()! * 1.75;
     var size = MediaQuery.of(context).size;
@@ -234,6 +237,9 @@ class _GalleryModeState extends State<_GalleryMode>
 
   @override
   void handleLongPressUp(Offset location) {
+    if(!appdata.settings['enableLongPressToZoom']) {
+      return;
+    }
     var photoViewController = photoViewControllers[reader.page]!;
     double target = photoViewController.getInitialScale!.call()!;
     photoViewController.animateScale?.call(target);
@@ -509,6 +515,9 @@ class _ContinuousModeState extends State<_ContinuousMode>
 
   @override
   void handleLongPressDown(Offset location) {
+    if(!appdata.settings['enableLongPressToZoom']) {
+      return;
+    }
     double target = photoViewController.getInitialScale!.call()! * 1.75;
     var size = MediaQuery.of(context).size;
     photoViewController.animateScale?.call(
@@ -519,6 +528,9 @@ class _ContinuousModeState extends State<_ContinuousMode>
 
   @override
   void handleLongPressUp(Offset location) {
+    if(!appdata.settings['enableLongPressToZoom']) {
+      return;
+    }
     double target = photoViewController.getInitialScale!.call()!;
     photoViewController.animateScale?.call(target);
   }

lib/pages/settings/reader.dart

@@ -54,6 +54,13 @@ class _ReaderSettingsState extends State<ReaderSettings> {
             widget.onChanged?.call("autoPageTurningInterval");
           },
         ).toSliver(),
+        _SwitchSetting(
+          title: 'Long press to zoom'.tl,
+          settingKey: 'enableLongPressToZoom',
+          onChanged: () {
+            widget.onChanged?.call('enableLongPressToZoom');
+          },
+        ).toSliver(),
       ],
     );
   }