fix: make the new nsview as the first responder.

Make the new view as the first responder(focused) so the new view can
accept events from input method.

Fixes #3968.

gdk/macos/gdkmacosglcontext.c

@@ -145,6 +145,7 @@ ensure_gl_view (GdkMacosGLContext *self)
       [nsview setPostsFrameChangedNotifications: YES];
       [nsview setNeedsDisplay:YES];
       [nswindow setContentView:nsview];
+      [nswindow makeFirstResponder:nsview];
       [nsview release];
 
       if (self->dummy_view != NULL)