[ExportVerilog] Incorrect verilog output for bitcast + zero width aggregate types

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We are emitting zero bit width array/struct as one bit element. This is problem when we use bitcast for them.

```mlir
hw.module @top(%source: i1) -> (b: !hw.struct, c: i1>) {
%cast = hw.bitcast %source: (i1) -> !hw.struct, c: i1>
hw.output %cast : !hw.struct, c: i1>
}
```

```sv
module top( // out.mlir:2:3
input source,
output struct packed {logic [0:0]/*Zero Width*/ zero; logic c; } b);

assign b = source; // out.mlir:3:12, :4:5
endmodule
```

Start with the ExportVerilog path that lowers the provided MLIR bitcast involving a zero-width array and struct, and reproduce the example from the issue. Trace how zero-width aggregate fields are represented in the generated SystemVerilog. Done means the example no longer emits a one-bit [0:0] field for the zero-width aggregate.

Written by the indexing model from the issue text.