Separate vndk_snapshot_package from vndk_package

vndk_package only includes current VNDK builds without snapshots.
The snapshots will be included by PRODUCT_EXTRA_VNDK_VERSIONS
regardless of vndk_package in PRODUCT_PACKAGES.

Bug: 71609233
Test: Generate snapshot files and include the version in
      PRODUCT_EXTRA_VNDK_VERSIONS. Check if snapshots are installed.

Change-Id: If788af2f7773dd50b8b9ceb1957b8e54fde9ca9f