Extract FakeInputReceiver and FakeInputWindow into a separate cpp file

It will be used by other tests that will be added in the future.

Bug: 210460522
Test: build
Change-Id: I2dfc9f2db73262e0e0a587940cbf513d697cc1c9
diff --git a/services/inputflinger/tests/Android.bp b/services/inputflinger/tests/Android.bp
index d389a0a..6ae9790 100644
--- a/services/inputflinger/tests/Android.bp
+++ b/services/inputflinger/tests/Android.bp
@@ -27,6 +27,7 @@
     name: "inputdispatcher_common_test_sources",
     srcs: [
         "FakeInputDispatcherPolicy.cpp",
+        "FakeWindows.cpp",
     ],
 }