Move drag event to InputDispatcher (5/n)

This CL add 'notifyDropWindow' to tell the policy about the dropping
window has been detected. That could help the drag controller to handle
the drop event and dispatch the clip data to the corresponding client.

Bug: 158242495
Test: atest inputflinger_tests
Change-Id: If7bce072dff5bdacb7eb765f94eb73ed63a58170
diff --git a/services/inputflinger/benchmarks/InputDispatcher_benchmarks.cpp b/services/inputflinger/benchmarks/InputDispatcher_benchmarks.cpp
index b2ddb42..7bd0c6b 100644
--- a/services/inputflinger/benchmarks/InputDispatcher_benchmarks.cpp
+++ b/services/inputflinger/benchmarks/InputDispatcher_benchmarks.cpp
@@ -113,6 +113,8 @@
 
     void setPointerCapture(bool enabled) override {}
 
+    void notifyDropWindow(const sp<IBinder>&, float x, float y) override {}
+
     InputDispatcherConfiguration mConfig;
 };