fix: ensure scrollbars are enabled by default

Author: aleclarson

React/Views/ScrollView/RCTScrollView.m

@@ -180,6 +180,9 @@ - (instancetype)initWithEventDispatcher:(RCTEventDispatcher *)eventDispatcher
     _cachedChildFrames = [NSMutableArray new];
     _lastClippedToRect = CGRectNull;
 
+    self.hasVerticalScroller = YES;
+    self.hasHorizontalScroller = YES;
+    
     // Note: This also makes "opaque" return NO.
     [self setDrawsBackground:NO];