TextInput: Fixed `textWasPaste` prop for singleline TextInput

Summary: This regression was recently introduced when RCTTextField was splitted into two classes.

Reviewed By: mmmulani

Differential Revision: D5313055

fbshipit-source-id: 1027ddeed7ea9a4bf6f30b0182092f42588b83e3

Libraries/Text/RCTUITextField.m

@@ -94,6 +94,14 @@
   return [self textRectForBounds:bounds];
 }
 
+#pragma mark - Overrides
+
+- (void)paste:(id)sender
+{
+  [super paste:sender];
+  _textWasPasted = YES;
+}
+
 #pragma mark - Layout
 
 - (CGSize)intrinsicContentSize