add symlink for compatibility (vndk apex)

With VNDK APEX, the location of VNDK lib is changed.
But vndk libs of older VNDK versions still depend on old location.

For current VNDK version, those hard-coded references will be fixed.
TODO(b/142911355): [VNDK APEX] Fix hard-coded references to /system/lib/vndk

Bug: 143192278
Bug: 142912195
Test: m com.android.vndk.current and check if /system/lib/vndk
      OVERRIDE_TARGET_FLATTEN_APEX m com.android.vndk.current

Change-Id: I2ebacde7fcd1c7621e4509e08a76765e1dfeb059