Rename "Debug Menu" title to "Dev Menu" on iOS

Summary:
We are (following a quick internal RFC) looking to standardise the term "[in-app] [Developer|Debug] menu" to "Dev Menu" in the React Native Debugging docs (and all docs references). (Indeed, the prevalent existing use in docs was already "Developer menu".) This PR aligns naming in the `RCTDevMenu` component on iOS.

See also facebook/react-native-website#3692.

Changelog:
[iOS][Changed] - Rename "Debug Menu" title to "Dev Menu"

Differential Revision: D44872456

fbshipit-source-id: 20eb1bbaff1b13be4090fda681d47557884ebd61

packages/react-native/React/CoreModules/RCTDevMenu.mm

@@ -428,10 +428,10 @@ - (void)setDefaultJSBundle
       ? UIAlertControllerStyleActionSheet
       : UIAlertControllerStyleAlert;
 
-  NSString *debugMenuType = self.bridge ? @"Bridge" : @"Bridgeless";
-  NSString *debugMenuTitle = [NSString stringWithFormat:@"React Native Debug Menu (%@)", debugMenuType];
+  NSString *devMenuType = self.bridge ? @"Bridge" : @"Bridgeless";
+  NSString *devMenuTitle = [NSString stringWithFormat:@"React Native Dev Menu (%@)", devMenuType];
 
-  _actionSheet = [UIAlertController alertControllerWithTitle:debugMenuTitle message:description preferredStyle:style];
+  _actionSheet = [UIAlertController alertControllerWithTitle:devMenuTitle message:description preferredStyle:style];
 
   NSArray<RCTDevMenuItem *> *items = [self _menuItemsToPresent];
   for (RCTDevMenuItem *item in items) {