fix(iOS): Inline code to find the webview's scrollView (#272)

Currently this works because of a category extension that adds a
`scrollView` method to every UIView instance, but that causes issues for
SwiftUI so we want to remove that extension from cordova-ios.

Since we do need to be able to look up the scrollView in this plugin, we
can just define a private local method that does the same thing in a way
that doesn't pollute global UIKit classes.

Ref: apache/cordova-ios#1400

src/ios/CDVStatusBar.m

@@ -25,6 +25,7 @@ Licensed to the Apache Software Foundation (ASF) under one
 
 #import "CDVStatusBar.h"
 #import <objc/runtime.h>
+#import <objc/message.h>
 #import <Cordova/CDVViewController.h>
 
 static const void *kHideStatusBar = &kHideStatusBar;
@@ -143,9 +144,9 @@ - (void)pluginInitialize
 
     setting  = @"StatusBarDefaultScrollToTop";
     if ([self settingForKey:setting]) {
-        self.webView.scrollView.scrollsToTop = [(NSNumber*)[self settingForKey:setting] boolValue];
+        [self webViewScrollView].scrollsToTop = [(NSNumber*)[self settingForKey:setting] boolValue];
     } else {
-        self.webView.scrollView.scrollsToTop = NO;
+        [self webViewScrollView].scrollsToTop = NO;
     }
 
     // blank scroll view to intercept status bar taps
@@ -462,6 +463,17 @@ - (void) dealloc
     [[NSNotificationCenter defaultCenter]removeObserver:self name:UIApplicationDidChangeStatusBarOrientationNotification object:nil];
 }
 
+- (UIScrollView *)webViewScrollView
+{
+    SEL scrollViewSelector = NSSelectorFromString(@"scrollView");
+
+    if ([self.webView respondsToSelector:scrollViewSelector]) {
+        return ((id (*)(id, SEL))objc_msgSend)(self.webView, scrollViewSelector);
+    }
+
+    return nil;
+}
+
 
 #pragma mark - UIScrollViewDelegate