[Thread] add Thread aconfig_declaration to java_sdk_library

This commit also moves Thread flags to Connectivity/common to ease
maintenance.

Test: m framework-connectivity-t
Bug: 317290555
Merged-In: I50f3d3b8205a5a9ee8154a649318a2c175edbb71
Merged-In: I8a71f4ee49cc68a9512f432e454469200f2a5058
Change-Id: I8a71f4ee49cc68a9512f432e454469200f2a5058
diff --git a/common/FlaggedApi.bp b/common/FlaggedApi.bp
index 449d7ae..56625c5 100644
--- a/common/FlaggedApi.bp
+++ b/common/FlaggedApi.bp
@@ -23,6 +23,14 @@
 }
 
 aconfig_declarations {
+    name: "com.android.net.thread.flags-aconfig",
+    package: "com.android.net.thread.flags",
+    container: "system",
+    srcs: ["thread_flags.aconfig"],
+    visibility: ["//packages/modules/Connectivity:__subpackages__"],
+}
+
+aconfig_declarations {
     name: "nearby_flags",
     package: "com.android.nearby.flags",
     container: "system",