[flang][debug] Add support for fixed size arrays. (#92568)

This PR adds the type conversion support for fixed size arrays. Mostly
mechanical changes converting dimension values to subrange fields. A
limitation is that lower bound is always one for the moment as that
information is missing in `SequenceType`.

With this change in place, I can evaluate fixed size arrays in debugger.
```

(gdb) p x
$1 = ((2, 3, 4, 5) (3, 4, 5, 6) (4, 5, 6, 7) (5, 6, 7, 8) (6, 7, 8, 9))
(gdb) ptype x
type = integer (4,5)
```

---------

Co-authored-by: Tom Eccles <t@freedommail.info>