tests: IBaz, nasty nesting struct

toString is broken in some cases because of recursive definitions. This
exercises that case.

Bug: 117342189
Test: hidl_test
Test: m android.hardware.tests.baz@1.0 android.hardware.tests.baz-V1.0-java
    (this runs hidl-gen on this for both Java and C++ output)
Test: manually inspected output

Change-Id: Ic09ac133345f2d83d6f83d3d0af1f63e7e3250ee