libvbmeta: add getter for rollback_index

This will be used by the derive_microdroid_vendor_dice_node binary in
the follow-up patch.

Bug: 287593065
Test: atest libvbmeta_rust.test
Change-Id: Ia38579a1038514190b98a5f1c82bab3bb509078b
diff --git a/libs/vbmeta/Android.bp b/libs/vbmeta/Android.bp
index 4fb6ae4..9a7375d 100644
--- a/libs/vbmeta/Android.bp
+++ b/libs/vbmeta/Android.bp
@@ -35,6 +35,8 @@
         ":avb_testkey_rsa2048",
         ":avb_testkey_rsa4096",
         ":avb_testkey_rsa8192",
+        ":test_microdroid_vendor_image",
+        ":test_microdroid_vendor_image_no_rollback_index",
     ],
     required: ["avbtool"],
     test_suites: ["general-tests"],