action-sheet [nfc]: Rename CopyButton to CopyMessageTextButton

The related localization string and parts of the related tests are also
renamed.

Note: The reason for this renaming is to have a clear distinction between
the existing "copy message text" and the upcoming "copy message link" buttons.

Author: sm-sayedi

assets/l10n/app_en.arb

@@ -43,8 +43,8 @@
   "@permissionsDeniedReadExternalStorage": {
     "description": "Message for dialog asking the user to grant permissions for external storage read access."
   },
-  "actionSheetOptionCopy": "Copy message text",
-  "@actionSheetOptionCopy":  {
+  "actionSheetOptionCopyMessageText": "Copy message text",
+  "@actionSheetOptionCopyMessageText":  {
     "description": "Label for copy message text button on action sheet."
   },
   "actionSheetOptionShare": "Share",

lib/widgets/action_sheet.dart

@@ -44,7 +44,7 @@ void showMessageActionSheet({required BuildContext context, required Message mes
           message: message,
           messageListContext: context,
         ),
-        CopyButton(message: message, messageListContext: context),
+        CopyMessageTextButton(message: message, messageListContext: context),
       ]);
     });
 }
@@ -330,8 +330,8 @@ class QuoteAndReplyButton extends MessageActionSheetMenuItemButton {
   };
 }
 
-class CopyButton extends MessageActionSheetMenuItemButton {
-  CopyButton({
+class CopyMessageTextButton extends MessageActionSheetMenuItemButton {
+  CopyMessageTextButton({
     super.key,
     required super.message,
     required super.messageListContext,
@@ -341,7 +341,7 @@ class CopyButton extends MessageActionSheetMenuItemButton {
 
   @override
   String label(ZulipLocalizations zulipLocalizations) {
-    return zulipLocalizations.actionSheetOptionCopy;
+    return zulipLocalizations.actionSheetOptionCopyMessageText;
   }
 
   @override get onPressed => (BuildContext context) async {

test/widgets/action_sheet_test.dart

@@ -449,15 +449,15 @@ void main() {
     });
   });
 
-  group('CopyButton', () {
+  group('CopyMessageTextButton', () {
     setUp(() async {
       TestDefaultBinaryMessengerBinding.instance.defaultBinaryMessenger.setMockMethodCallHandler(
         SystemChannels.platform,
         MockClipboard().handleMethodCall,
       );
     });
 
-    Future<void> tapCopyButton(WidgetTester tester) async {
+    Future<void> tapCopyMessageTextButton(WidgetTester tester) async {
       await tester.ensureVisible(find.byIcon(Icons.copy, skipOffstage: false));
       await tester.tap(find.byIcon(Icons.copy));
       await tester.pump(); // [MenuItemButton.onPressed] called in a post-frame callback: flutter/flutter@e4a39fa2e
@@ -469,7 +469,7 @@ void main() {
       final store = await testBinding.globalStore.perAccount(eg.selfAccount.id);
 
       prepareRawContentResponseSuccess(store, message: message, rawContent: 'Hello world');
-      await tapCopyButton(tester);
+      await tapCopyMessageTextButton(tester);
       await tester.pump(Duration.zero);
       check(await Clipboard.getData('text/plain')).isNotNull().text.equals('Hello world');
     });
@@ -480,7 +480,7 @@ void main() {
       final store = await testBinding.globalStore.perAccount(eg.selfAccount.id);
 
       prepareRawContentResponseError(store);
-      await tapCopyButton(tester);
+      await tapCopyMessageTextButton(tester);
       await tester.pump(Duration.zero); // error arrives; error dialog shows
 
       await tester.tap(find.byWidget(checkErrorDialog(tester,