Add "unknown" state for unions passed to opaque functions #801

Job	Run time
ubu-24 \| g++-14 \| c++2b \| libstdc++ \| ubuntu-24.04	6m 2s
ubu-24 \| g++-13 \| c++2b \| libstdc++ \| ubuntu-24.04	5m 33s
ubu-20 \| g++-10 \| c++20 \| libstdc++ \| ubuntu-20.04	5m 11s
ubu-24 \| clang++-18 \| c++20 \| libstdc++ \| ubuntu-24.04	7m 5s
ubu-24 \| clang++-18 \| c++23 \| libc++-18-dev \| ubuntu-24.04	16s
ubu-22 \| clang++-15 \| c++20 \| libstdc++ \| ubuntu-22.04	5m 35s
ubu-22 \| clang++-15 \| c++20 \| libc++-15-dev \| ubuntu-22.04	5m 28s
ubu-20 \| clang++-12 \| c++20 \| libstdc++ \| ubuntu-20.04	4m 46s
mac-14 \| clang++ \| c++2b \| default \| macos-14	12s
mac-13 \| clang++ \| c++2b \| default \| macos-13	8m 19s
mac-13 \| clang++-15 \| c++2b \| default \| macos-13	9m 2s
win-22 \| cl.exe \| c++latest \| default \| windows-2022	4m 23s
win-22 \| cl.exe \| c++20 \| default \| windows-2022	4m 17s
aggregate-results	7s
	1h 6m 16s

Provide feedback