[BUG]: Non-structural types can't be passed in `constant`

Non-structural types can't be passed as NTTP, thus extended floating point types like `__half` or `__nv_bfloat16` can't be passed in `constant`. For example ([link](https://godbolt.org/z/j9r9dznP9)):
```cpp
#include
#include
#include

#include

int main()
{
[[maybe_unused]] cuda::__argument::__constant::max()> constant{};
}
```
fails to compile.

We could make this work using mechanism described in #9273