[ExportVerilog] Control names of output temporaries for instances

hw.instance doesn't have a way to store result names. If it did, legalize names could legalize the output value names (which eventually can become wires so the verilog instance has something to tie the outputs too), rather than waiting until export verilog.

Start by tracing the hw.instance result handling, name legalization, and ExportVerilog entry points described in the issue. Determine how result names could be retained and legalized before Verilog export; done means output temporaries receive controlled legal names without waiting until export.

Written by the indexing model from the issue text.