[flang][debug] Fix array lower bounds in derived type members. (#113183)

The lower bound information for the array members of a derived type
can't be obtained from the `DeclareOp`. It has to be extracted from the
`TypeInfoOp`. That was left as FIXME in the code. This PR adds the
missing functionality to fix the issue.

I tried the following approaches before settling on the current one that
is to generate `DITypeAttr` for array members right where the components
are being processed.

1. Generate a temp XDeclareOp with the shift information obtained from
the `TypeInfoOp`. This caused a few issues mostly related to
`unrealized_conversion_cast`.

2. Change the shift operands in the `declOp` that was passed in the
function before calling `convertType`. The code can be seen in the
abcf031a8e5a02f0081e7f293858302e7bf47bec. It essentially looked like the
following. It works correctly but I was not sure if temporarily changing
the `declOp` is the safe thing to do.

```
mlir::OperandRange originalShift = declOp.getShift();
mlir::MutableOperandRange mutableOpRange = declOp.getShiftMutable();
mutableOpRange.assign(shiftOpers);
elemTy = convertType(fieldTy, fileAttr, scope, declOp);
mutableOpRange.assign(originalShift);
```

Fixes #113178.

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