action_sheet [nfc]: Tighten button constructors onto one line

This is a nice small bonus from renaming the parameter that was
`messageListContext` to the shorter name `pageContext`.

Some of these don't quite fit in 80 columns.  But the details of
the parameter list are boring (because they're all the same),
so it's OK that some of them go a little over.

lib/widgets/action_sheet.dart

@@ -183,11 +183,7 @@ class MessageActionSheetCancelButton extends StatelessWidget {
 // This button is very temporary, to complete #125 before we have a way to
 // choose an arbitrary reaction (#388). So, skipping i18n.
 class AddThumbsUpButton extends MessageActionSheetMenuItemButton {
-  AddThumbsUpButton({
-    super.key,
-    required super.message,
-    required super.pageContext,
-  });
+  AddThumbsUpButton({super.key, required super.message, required super.pageContext});
 
   @override IconData get icon => ZulipIcons.smile;
 
@@ -223,11 +219,7 @@ class AddThumbsUpButton extends MessageActionSheetMenuItemButton {
 }
 
 class StarButton extends MessageActionSheetMenuItemButton {
-  StarButton({
-    super.key,
-    required super.message,
-    required super.pageContext,
-  });
+  StarButton({super.key, required super.message, required super.pageContext});
 
   @override IconData get icon => _isStarred ? ZulipIcons.star_filled : ZulipIcons.star;
 
@@ -320,11 +312,7 @@ Future<String?> fetchRawContentWithFeedback({
 }
 
 class QuoteAndReplyButton extends MessageActionSheetMenuItemButton {
-  QuoteAndReplyButton({
-    super.key,
-    required super.message,
-    required super.pageContext,
-  });
+  QuoteAndReplyButton({super.key, required super.message, required super.pageContext});
 
   @override IconData get icon => ZulipIcons.format_quote;
 
@@ -380,11 +368,7 @@ class QuoteAndReplyButton extends MessageActionSheetMenuItemButton {
 }
 
 class MarkAsUnreadButton extends MessageActionSheetMenuItemButton {
-  MarkAsUnreadButton({
-    super.key,
-    required super.message,
-    required super.pageContext,
-  });
+  MarkAsUnreadButton({super.key, required super.message, required super.pageContext});
 
   @override IconData get icon => Icons.mark_chat_unread_outlined;
 
@@ -400,11 +384,7 @@ class MarkAsUnreadButton extends MessageActionSheetMenuItemButton {
 }
 
 class CopyMessageTextButton extends MessageActionSheetMenuItemButton {
-  CopyMessageTextButton({
-    super.key,
-    required super.message,
-    required super.pageContext,
-  });
+  CopyMessageTextButton({super.key, required super.message, required super.pageContext});
 
   @override IconData get icon => ZulipIcons.copy;
 
@@ -437,11 +417,7 @@ class CopyMessageTextButton extends MessageActionSheetMenuItemButton {
 }
 
 class CopyMessageLinkButton extends MessageActionSheetMenuItemButton {
-  CopyMessageLinkButton({
-    super.key,
-    required super.message,
-    required super.pageContext,
-  });
+  CopyMessageLinkButton({super.key, required super.message, required super.pageContext});
 
   @override IconData get icon => Icons.link;
 
@@ -467,11 +443,7 @@ class CopyMessageLinkButton extends MessageActionSheetMenuItemButton {
 }
 
 class ShareButton extends MessageActionSheetMenuItemButton {
-  ShareButton({
-    super.key,
-    required super.message,
-    required super.pageContext,
-  });
+  ShareButton({super.key, required super.message, required super.pageContext});
 
   @override
   IconData get icon => defaultTargetPlatform == TargetPlatform.iOS