Enable exact type checks with HPy_TypeCheck

[fangerer]

In CPython, there are usually macros like:

#define PySomething_Check(op) PyObject_TypeCheck(op, &PySomething_Type)
#define PySomething_CheckExact(op) (Py_TYPE(op) == &PySomething_Type)

That translates to following in HPy:

// PySomething_Check
HPy_TypeCheck(ctx, h_obj, h_type)

// PySomething_CheckExact(op)
HPy_Is(ctx, HPy_Type(ctx, h_obj), h_type)

As it turns out, the exact type check is pretty verbose in HPy and having two API calls may also be a high performance drawback.

An alternative approach would be to have a new API for that. Something like HPy_TypeCheckExact (which would come with a new context function as well).