[CUDA][HIP] allow trivial ctor/dtor in device var init (#73140)

Treat ctor/dtor in device var init as host device function
so that they can be used to initialize file-scope
device variables to match nvcc behavior. If they are non-trivial
they will be diagnosed.

We cannot add implicit host device attrs to non-trivial
ctor/dtor since determining whether they are non-trivial
needs to know whether they have a trivial body and all their
member and base classes' ctor/dtor have trivial body, which
is affected by where their bodies are defined or instantiated.

Fixes: #72261

Fixes: SWDEV-432412