Throw custom errors from spawn

[lukekarrys]

Implements some custom error subclasses that get thrown by spawn when known or unknown git errors occur.

Then in packages like pacote we can do something like:

if (er instanceof git.errors.GitPathspecError) {
  // We know what happened so we can rethrow knowing we shouldn't try anything else
  // and that we'll get a more helpful error message
  throw er
}

Details

• Each custom error class message is replaced with a helpful message (eg The git reference could not be found.) followed by the full error form @npmcli/promise-spawn available via er.stderr (which gets printed by the cli error handler)
• The rest of the enumerable properties from @npmcli/promise-spawn are assigned to the custom error
• Wrapped the previous retry logic into a new error subclass which might be useful to handle differently in other error handlers in the future

TODO

• Finish implementing tests

[wraithgar]

I like this. It solves two problems, the first is "how do we tell the user what actually went wrong in a clear way" and the other is "how do we allow pactote to programmatically know how to react to certain errors.

[wraithgar]

I think this is shippable

[nlf]

this looks great