macOS: Allow NSView subclasses to accept first mouse event.

This brings the behavior in line with Windows and Linux. Going between
multiple windows now doesn't use the first click only to change focus
but also allows Blender to process those events.

intern/ghost/intern/GHOST_WindowViewCocoa.h

@@ -58,6 +58,11 @@
   return YES;
 }
 
+- (BOOL)acceptsFirstMouse:(NSEvent *)event
+{
+  return YES;
+}
+
 // The trick to prevent Cocoa from complaining (beeping)
 - (void)keyDown:(NSEvent *)event
 {