[fabric] Make text input resign first responder through the window in…

…stance

Summary:
Fix AppKit exception throws when blurring text inputs by calling `resignFirstResponder` directly on the backing text input view.
Resigning the first responder state has to happen through the window by calling `[window makeFirstResponder:nil]` which will:
- call `resignFirstResponder` on the current first responder
- if successful, the window will become the first responder

Test Plan:
- Run Zeratul with Fabric
- Focus the search text input above the message threads
- Click inside the active message thread to trigger the auto-focus of the composer and the blur on the search field
- The focused field resigns the first responder status without throwing an exception

 https://pxl.cl/3GvZD

Reviewers: shawndempsey, #rn-desktop

Reviewed By: shawndempsey

Differential Revision: https://phabricator.intern.facebook.com/D50700782

packages/react-native/React/Fabric/Mounting/ComponentViews/TextInput/RCTTextInputComponentView.mm

@@ -552,7 +552,15 @@ - (void)focus
 
 - (void)blur
 {
+#if !TARGET_OS_OSX // [macOS]
   [_backedTextInputView resignFirstResponder];
+#else // [macOS
+  NSWindow *window = _backedTextInputView.window;
+  if (window && window.firstResponder == _backedTextInputView) {
+    // Calling makeFirstResponder with nil will call resignFirstResponder and make the window the first responder
+    [window makeFirstResponder:nil];
+  }
+#endif // macOS];
 }
 
 - (void)setTextAndSelection:(NSInteger)eventCount