[ANativeWindow] Add ANativeWindow_allocateBuffers stable abi.

Bug: 137012798
Test: builds
Change-Id: Ibe2afe83d48adb583bfbda088376fcf402050814
diff --git a/libs/nativewindow/include/system/window.h b/libs/nativewindow/include/system/window.h
index a4e5afd..121374b 100644
--- a/libs/nativewindow/include/system/window.h
+++ b/libs/nativewindow/include/system/window.h
@@ -252,6 +252,7 @@
     NATIVE_WINDOW_SET_DEQUEUE_INTERCEPTOR         = 42,    /* private */
     NATIVE_WINDOW_SET_PERFORM_INTERCEPTOR         = 43,    /* private */
     NATIVE_WINDOW_SET_QUEUE_INTERCEPTOR           = 44,    /* private */
+    NATIVE_WINDOW_ALLOCATE_BUFFERS                = 45,    /* private */
     // clang-format on
 };