mark window declaration as exportable

window declarations includes exported flags. It's declarations should be
marked as exportable to make sure the framework will jarjar this flag
class.

Bug: 357519755
Test: presbumit
Flag: n/a
Change-Id: If69a13fc0d453fa23bb4c6b7c46f2738edabdd87
diff --git a/AconfigFlags.bp b/AconfigFlags.bp
index 7d9e95b..4e34b63 100644
--- a/AconfigFlags.bp
+++ b/AconfigFlags.bp
@@ -172,6 +172,7 @@
 // Window
 aconfig_declarations {
     name: "com.android.window.flags.window-aconfig",
+    exportable: true,
     package: "com.android.window.flags",
     container: "system",
     srcs: ["core/java/android/window/flags/*.aconfig"],