Add flag for setFrameRate API

Bug: 356987016
Test: presubmits, local config test
Flag: com.android.graphics.surfaceflinger.flags.arr_setframerate_api

Change-Id: If0856aea1277c5e05921138de7a1c12a95cb3f46

Author: Rachel Lee

services/surfaceflinger/surfaceflinger_flags_new.aconfig

@@ -10,6 +10,14 @@ flag {
   bug: "284324521"
 } # adpf_gpu_sf
 
+flag {
+  name: "arr_setframerate_api"
+  namespace: "core_graphics"
+  description: "New setFrameRate API for Android 16"
+  bug: "356987016"
+  is_fixed_read_only: true
+} # arr_setframerate_api
+
 flag {
   name: "ce_fence_promise"
   namespace: "window_surfaces"