SF: Compile with -Wextra

Compile with -Wextra for additional conversion checks. In each file
which produces compile errors -Wextra is ignored.

Bug: 175126758
Test: m surfaceflinger && m libsurfaceflinger_unittest
Change-Id: Iec6bcc699715a99c8c65d891ab3c0481e884c728
diff --git a/services/surfaceflinger/tests/DetachChildren_test.cpp b/services/surfaceflinger/tests/DetachChildren_test.cpp
index 9c7b1fc..abf8b1a 100644
--- a/services/surfaceflinger/tests/DetachChildren_test.cpp
+++ b/services/surfaceflinger/tests/DetachChildren_test.cpp
@@ -371,4 +371,7 @@
     }
 }
 
-} // namespace android
\ No newline at end of file
+} // namespace android
+
+// TODO(b/129481165): remove the #pragma below and fix conversion issues
+#pragma clang diagnostic pop // ignored "-Wconversion"
\ No newline at end of file