Use enum class for injection constants

To improve code completion and error outputs from gtest, use enum class
for injection mode and injection result

Bug: none
Test: presubmit
Change-Id: I579a3da95c0d20375e155fd52d426e2460fdffa0
diff --git a/services/inputflinger/dispatcher/InjectionState.cpp b/services/inputflinger/dispatcher/InjectionState.cpp
index b2d0a26..c8024a6 100644
--- a/services/inputflinger/dispatcher/InjectionState.cpp
+++ b/services/inputflinger/dispatcher/InjectionState.cpp
@@ -24,7 +24,7 @@
       : refCount(1),
         injectorPid(injectorPid),
         injectorUid(injectorUid),
-        injectionResult(INPUT_EVENT_INJECTION_PENDING),
+        injectionResult(android::os::InputEventInjectionResult::PENDING),
         injectionIsAsync(false),
         pendingForegroundDispatches(0) {}