[flang][runtime] Establish derived type desc properly. (#67623)

Example:
```
module types
  type t
     real,allocatable :: c
  end type t
contains
  function h(x)
    class(t),allocatable :: h
    ...
  end function h
  subroutine test
    type(t),allocatable :: b(:)
    allocate(b(2),source=h(2.5))
  end subroutine test7
end module type
```

`DoFromSourceAssign` creates two descriptors for initializing
`b(1)` and `b(2)` from the result of `h`. This Create call
creates a descriptor without properly initialized addendum,
so the Assign just does shallow copies of the descriptor
representing result of `h` into `b(1)` and `b(2)`.

I modified Create code to properly establish the descriptor
for derived type case.

I had to keep the `addendum` argument to keep the testing
in `flang/unittests/Runtime/TemporaryStack.cpp`.