Add interactive mode to scripts/rubocop-parse

What does this MR do and why?

The startup of scripts/rubocop-parse is slow due to RuboCop etc.

With the interactive mode you can do sessions like:

  $ scripts/rubocop-parse -i
  Ruby version: 2.7

  Use `ast(source_string, version: nil)` method to parse code and output AST. For example:
    ast('puts :hello')

  >> ast("puts 1 + 1")
  (send nil :puts
    (send
      (int 1) :+
      (int 1)))
  => nil
  >> ast(%{class Foo; end})
  (class
    (const nil :Foo) nil nil)
  => nil
  >>

Screenshots or screen recordings

$ scripts/rubocop-parse
Usage: scripts/rubocop-parse [-e code] [FILE...]
    -e, --eval FRAGMENT              Process a fragment of Ruby code
    -i, --interactive
    -v, --ruby-version RUBY_VERSION  Parse as Ruby would. Defaults to RuboCop TargetRubyVersion setting.
    -h, --help

$ scripts/rubocop-parse -e "puts 1"
(send nil :puts
  (int 1))

$ scripts/rubocop-parse app/models/error_tracking.rb
(module
  (const nil :ErrorTracking)
  (defs
    (self) :table_name_prefix
    (args)
    (str "error_tracking_")))

$ scripts/rubocop-parse -i
Ruby version: 2.7

Use `ast(source_string, version: nil)` method to parse code and output AST. For example:
  ast('puts :hello')

>> ast("1 + 2")
(send
  (int 1) :+
  (int 2))
=> nil
>> ast("class Foo; end")
(class
  (const nil :Foo) nil nil)
=> nil
>>
>>

How to set up and validate locally

See above.

MR acceptance checklist

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