Do not export private headers with llndk library

A header file in private directory are not supposed to export with
llndk library. To avoid this, move the private directory to a new
include-private directory and export it for framework-only library.

Bug: 69235725
Test: build and boot any device.
Change-Id: I9f020411350cf5b5f1db01ef9add76d8c3b2c395
diff --git a/libs/nativewindow/Android.bp b/libs/nativewindow/Android.bp
index 64eb110..aa116bf 100644
--- a/libs/nativewindow/Android.bp
+++ b/libs/nativewindow/Android.bp
@@ -30,7 +30,10 @@
 
 cc_library {
     name: "libnativewindow",
-    export_include_dirs: ["include"],
+    export_include_dirs: [
+        "include",
+        "include-private",
+    ],
 
     clang: true,