Use std::filesystem for input event devices scan.

Use std::filesystem directory iterator to scan event devices in EventHub.

Bug: 160010896
Test: atest inputflinger_tests, atest EventHubTest
Change-Id: Ib5658e96783b8a1099fe0a2cb6dda51703045c84
diff --git a/services/inputflinger/tests/Android.bp b/services/inputflinger/tests/Android.bp
index eae0963..eb9ac68 100644
--- a/services/inputflinger/tests/Android.bp
+++ b/services/inputflinger/tests/Android.bp
@@ -44,5 +44,8 @@
             "frameworks/native/libs/input",
         ],
     },
+    static_libs: [
+        "libc++fs"
+    ],
     require_root: true,
 }