Simplify concatenations and selects throughout a module.
This is a mainly aesthetic transform that applies vl-expr-clean-selects throughout modules. This may help to make certain concatenation and select expressions more readable.
Implementation-wise, this is the usual boilerplate to extend vl-expr-clean-selects through the parse tree, except that we aren't going to go through ranges: we only do this in assignments, instances, and statements, where we expect to see wires.