[Thread] add aconfig_declarations for Thread module API flags

This is required to included Thread module APIs in DP2 release.
See ag/26286387

merged-in is used to stop the CL from being merged into U branches

Bug: 325886480
Merged-In: I1eed7982b40d28947aa3f9575c568eac325dc832
Merged-In: I79be1b48058ce6fb08149e18cdd7a5f5b0762769
Change-Id: I79be1b48058ce6fb08149e18cdd7a5f5b0762769

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.
+//
+
+aconfig_declarations {
+    name: "com.android.net.thread.flags-aconfig",
+    package: "com.android.net.thread.flags",
+    container: "system",
+    srcs: ["thread_base.aconfig"],
+    visibility: ["//packages/modules/Connectivity:__subpackages__"],
+}