Create `api_for_backported_fixes` flag.

This flag is used to guard the Build.getCriticalFixStatus API.

Flag: android.os.api_for_backported_fixes
Bug: 308461809
Test: m framwork-all
Change-Id: I6437ce09419876f4cc6ddc1eef02360bc5693d03
diff --git a/core/java/android/os/flags.aconfig b/core/java/android/os/flags.aconfig
index 16cb66e..81987907 100644
--- a/core/java/android/os/flags.aconfig
+++ b/core/java/android/os/flags.aconfig
@@ -240,3 +240,11 @@
     is_fixed_read_only: true
     bug: "370845648"
 }
+
+flag {
+    name: "api_for_backported_fixes"
+    namespace: "media_reliability"
+    description: "Public API app developers use to check if a known issue is fixed on a device."
+    bug: "308461809"
+    is_exported: true
+}