[fabric] Add responder property to backing text input view protocol

Summary:
Add a `responder` property to support assigning the first responder to the actual textfield/textview if the view is wrapped or not.

The wrapped text view already implements this property. This diff brings the same functionality to the text field and declares it on the common protocol.

Test Plan: Tested later in this stack.

Reviewers: shawndempsey, chpurrer, #rn-desktop

Reviewed By: shawndempsey, chpurrer

Differential Revision: https://phabricator.intern.facebook.com/D51962395

Tasks: T167538822, T157889591

Author: Nick Lefever

packages/react-native/Libraries/Text/TextInput/RCTBackedTextInputViewProtocol.h

@@ -38,6 +38,7 @@ NS_ASSUME_NONNULL_BEGIN
 @property (nonatomic, assign, readonly) BOOL textWasPasted;
 #else // [macOS
 @property (nonatomic, assign) BOOL textWasPasted;
+@property (nonatomic, readonly) NSResponder *responder;
 #endif // macOS]
 @property (nonatomic, assign, readonly) BOOL dictationRecognizing;
 @property (nonatomic, assign) UIEdgeInsets textContainerInset;

packages/react-native/Libraries/Text/TextInput/Singleline/RCTUITextField.mm

@@ -217,6 +217,11 @@ - (void)setTextContainerInset:(UIEdgeInsets)textContainerInset
 
 #if TARGET_OS_OSX // [macOS
 
+- (NSResponder *)responder
+{
+  return self;
+}
+
 + (Class)cellClass
 {
   return RCTUITextFieldCell.class;