Add generic progress machinery for operations in `jco-transpile`

[vados-cosmonic]

As part of jco code (when transpile was included), operations in jco-transpile would manipulate spinners and do a bit to keep the user updated as to progress.

Before jco-transpile can completely replace the code in jco, it would be good to reintroduce the ability to detect and report on progress from functions exported by jco-transpile. This is obviously quite implementation specific and finnicky to get right for the caller, but a simple onProgress callback passed in might be enough.

There are two places (at least) that progress needs to be reportable:

• opt.js
• transpile.js

See #773 for places where the spinner was used.

[vados-cosmonic]

Another thing that should likely get done as part of this issue is detecting and offering improved error messages at the CLI level (see PR), printWITLayoutHint should be able to run based on errors that are thrown from typegen.js code.