Move things in InputWindowInfo to enum classes

Also introduce a new Flag class to make it possible to deal with flags
while treating the individual flags as part of an enum class in a type
safe manner.

Bug: 160010896
Test: atest inputflinger_tests, atest libinput_tests
Change-Id: I915a1c1e3b31f1c0fd99b83ba5fad7e537cd6f84
diff --git a/libs/input/tests/Android.bp b/libs/input/tests/Android.bp
index 3b57146..9782c1a 100644
--- a/libs/input/tests/Android.bp
+++ b/libs/input/tests/Android.bp
@@ -2,6 +2,7 @@
 cc_test {
     name: "libinput_tests",
     srcs: [
+        "Flags_test.cpp",
         "IdGenerator_test.cpp",
         "InputChannel_test.cpp",
         "InputDevice_test.cpp",