Fix TextInput numeric keyboard submit

Summary:
When you have a numeric non-multiline `TextInput` and a `returnKeyType` is `done` we automatically add an input accessory view ([implementation](603cc48ceb/Libraries/Text/RCTTextInput.m (L269)#L315)).

That view has a done button which triggers [handleInputAccessoryDoneButton](603cc48ceb/Libraries/Text/RCTTextInput.m (L317...L320)) which currently directly sends `endEditing:` to the text field / text view. As a consequence, the [textInputShouldReturn](603cc48ceb/Libraries/Text/RCTTextInput.m (L118...L121)) is not called and we dismiss the keyboard even if the `blurOnSubmit` value is `false`.

Confirm that the keyboard is not dismissed when you tap on Done button on this `TextInput`:
```
<TextInput
  keyboardType={'numeric'}
  returnKeyType={'done'}
  blurOnSubmit={false}
/>
```

and that the keyboard is dismissed for this `TextInput`:
```
<TextInput
  keyboardType={'numeric'}
  returnKeyType={'done'}
  blurOnSubmit
/>
```
Closes https://github.com/facebook/react-native/pull/15438

Differential Revision: D5601462

Pulled By: javache

fbshipit-source-id: 24e4048e2e66d1a42fa97d83b4a3eb61e5d817ea

Libraries/Text/RCTTextInput.m

@@ -316,7 +316,9 @@ RCT_NOT_IMPLEMENTED(- (instancetype)initWithFrame:(CGRect)frame)
 
 - (void)handleInputAccessoryDoneButton
 {
-  [self.backedTextInputView endEditing:YES];
+  if ([self textInputShouldReturn]) {
+    [self.backedTextInputView endEditing:YES];
+  }
 }
 
 @end