chore(iOS): Rename RNSUIBarButtonItem to RNSBackBarButtonItem (#3119)

## Description

From discussion in
#2987 (comment).
We should rename the class into something more specific because it
really does one specific thing.

## Changes

title

## Test code and steps to reproduce

No changes, disabling back button menu should still work. You can modify
BottomTabsTest / Tab4 with `screenOption={{ headerBackButtonMenuEnabled:
false }}`

Author: kmichalikk

ios/RNSScreenStackHeaderConfig.mm

@@ -25,12 +25,12 @@
 #import <React/RCTFont.h>
 #import <React/RCTImageLoader.h>
 #import <React/RCTImageSource.h>
+#import "RNSBackBarButtonItem.h"
 #import "RNSConvert.h"
 #import "RNSDefines.h"
 #import "RNSScreen.h"
 #import "RNSScreenStackHeaderConfig.h"
 #import "RNSSearchBar.h"
-#import "RNSUIBarButtonItem.h"
 
 #ifdef RCT_NEW_ARCH_ENABLED
 namespace react = facebook::react;
@@ -673,7 +673,7 @@ + (void)updateViewController:(UIViewController *)vc
 #if defined(__IPHONE_OS_VERSION_MAX_ALLOWED) && defined(__IPHONE_26_0) && \
     __IPHONE_OS_VERSION_MAX_ALLOWED >= __IPHONE_26_0
           if (@available(iOS 26.0, *)) {
-            // Workaround for missing search bar on root stack screen. 
+            // Workaround for missing search bar on root stack screen.
             // See: https://github.com/software-mansion/react-native-screens/pull/3098
             navitem.searchBarPlacementAllowsToolbarIntegration = NO;
           }
@@ -746,10 +746,10 @@ - (void)configureBackItem:(nullable UINavigationItem *)prevItem API_UNAVAILABLE(
   prevItem.backButtonDisplayMode = config.backButtonDisplayMode;
 
   if (config.isBackTitleVisible) {
-    RNSUIBarButtonItem *backBarButtonItem = [[RNSUIBarButtonItem alloc] initWithTitle:resolvedBackTitle
-                                                                                style:UIBarButtonItemStylePlain
-                                                                               target:nil
-                                                                               action:nil];
+    RNSBackBarButtonItem *backBarButtonItem = [[RNSBackBarButtonItem alloc] initWithTitle:resolvedBackTitle
+                                                                                    style:UIBarButtonItemStylePlain
+                                                                                   target:nil
+                                                                                   action:nil];
     auto shouldUseCustomBackBarButtonItem = config.disableBackButtonMenu;
     [backBarButtonItem setMenuHidden:config.disableBackButtonMenu];
 

ios/utils/RNSUIBarButtonItem.h renamed to ios/utils/RNSBackBarButtonItem.h

@@ -1,6 +1,6 @@
 #import <UIKit/UIKit.h>
 
-@interface RNSUIBarButtonItem : UIBarButtonItem
+@interface RNSBackBarButtonItem : UIBarButtonItem
 
 @property (nonatomic) BOOL menuHidden;
 

ios/utils/RNSUIBarButtonItem.mm renamed to ios/utils/RNSBackBarButtonItem.mm

@@ -1,6 +1,6 @@
-#import "./RNSUIBarButtonItem.h"
+#import "./RNSBackBarButtonItem.h"
 
-@implementation RNSUIBarButtonItem
+@implementation RNSBackBarButtonItem
 
 - (void)setMenuHidden:(BOOL)menuHidden
 {