[Thread] add Android.bp for Thread flags

This is not required for code in the mainline module since the flag
infra is not supported for mainline. But we will need to write code
in UserManager and it needs to be guarded by new Thread flags.

Note that Merged-In is added to skip merging this CL into the
udc-mainline-prod branch because trunk stable flagging is not supported
there

Bug: 307679182
Test: m
Merged-In: I88c993680976d2e10d672bfdbf45119f2db13868
Change-Id: Id53fa3e7c9592b04f37f4cbd7dcd0499859e59ed

thread/flags/Android.bp

+//
+// Copyright (C) 2024 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+package {
+    default_applicable_licenses: ["Android-Apache-2.0"],
+}
+
+aconfig_declarations {
+    name: "thread_aconfig_flags",
+    package: "com.android.net.thread.flags",
+    srcs: ["thread_base.aconfig"],
+}
+
+java_aconfig_library {
+    name: "thread_aconfig_flags_lib",
+    aconfig_declarations: "thread_aconfig_flags",
+    min_sdk_version: "30",
+    apex_available: [
+        "//apex_available:platform",
+        "com.android.tethering",
+    ],
+}