Refactor the parsing/printing of the top-level module.

This changes the top-level module parser to handle the case where the top-level module is defined with the module operation syntax, i.e:
  module ... {
  }

The printer is also updated to always print the top-level module in this form. This allows for cleanly round-tripping the location and attributes of the top-level module.

PiperOrigin-RevId: 257492069