TextInput on iOS: Fixing selectAll feature for multiline text input

Summary:
`selectAll:` does not work for UITextView when it's being called inside UITextView's delegate methods.

This is a bug in UIKit and this quite ugly workaround is only a known solution for it.

Changelog: [Bug][iOS] Fixed bug in implementation of <TextInput>'s selectOnFocus prop

Reviewed By: sammy-SC

Differential Revision: D18966755

fbshipit-source-id: 2ba15fa94570d463a2ea3490331fb879611dc6b8

Author: shergin

Libraries/Text/TextInput/Multiline/RCTUITextView.m

@@ -180,6 +180,17 @@ - (void)setContentOffset:(CGPoint)contentOffset animated:(__unused BOOL)animated
   [super setContentOffset:contentOffset animated:NO];
 }
 
+- (void)selectAll:(id)sender
+{
+  [super selectAll:sender];
+
+  // `selectAll:` does not work for UITextView when it's being called inside UITextView's delegate methods.
+  dispatch_async(dispatch_get_main_queue(), ^{
+    UITextRange *selectionRange = [self textRangeFromPosition:self.beginningOfDocument toPosition:self.endOfDocument];
+    [self setSelectedTextRange:selectionRange notifyDelegate:NO];
+  });
+}
+
 #pragma mark - Layout
 
 - (CGFloat)preferredMaxLayoutWidth