Migrate pretty print to Prism

[palkan]

Context

Action Policy provides a useful pretty printing functionality that helps to see why the policy rule returns true or false:

irb> pp :feed?

MyPolicy#feed?
↳ (
    admin? #=> false
    OR
    allowed_to?(:access_feed?) #=> true
  )
  AND
  (
    user.name == "Jack" #=> false
    OR
    user.name == "Kate" #=> true
  )

Currently, it relies on Parse and Unparser gems; thus, requiring these libraries to present in the bundle to work. With Prism, we should be able to achieve the same behavior without any third-party dependencies.

TODO

Refactor utils/pretty_print to use Prism:

• Prism Ruby API (it uses the same Visitor pattern that we already use with Parser)

• Instead of unparsing, we can obtained the original source code string from node.location (using source[loc.start_offset...loc.end_offset]).