[ios, macos] Use common instead of default mode for run loop source (#5503)

The map events instigated by certain actions
(i.e. updates from a UIScrollView) are not processed by the run loop
with `kCFRunLoopDefaultMode`until the thread is idle. This changes
the mode to `kCFRunLoopCommonModes` to avoid this issue.

platform/darwin/src/async_task.cpp

@@ -25,7 +25,7 @@ public:
             perform
         };
         source = CFRunLoopSourceCreate(kCFAllocatorDefault, 0, &context);
-        CFRunLoopAddSource(loop, source, kCFRunLoopDefaultMode);
+        CFRunLoopAddSource(loop, source, kCFRunLoopCommonModes);
     }
 
     ~Impl() {