[flang][cuda] Include constant extents in cuf.alloc size computation (#194288)
Example:
```fortran
real, device :: arr(n, 4, m)
```
For arrays with mixed constant and dynamic extents
(`!fir.array<?x4x?xf32>`), the allocation size only includes the dynamic
extents (`n * m * 4 bytes`), missing the constant extent `4`. This
under-allocates by a factor of 4, causing `cudaErrorIllegalAddress`.
Fix: After multiplying the dynamic extents, also multiply in constant
extents from the type, producing the correct size (`n * m * 4 * 4
bytes`).