Summarize inspect

[marcandre]

The current inspect methods for most classes are not very usable:

  @corrector=
   #<Parser::Source::TreeRewriter:0x00007fd280304148
    @action_root=
     #<Parser::Source::TreeRewriter::Action:0x00007fd280d73d90
      @children=[],
      @enforcer=
       #<Method: RuboCop::Cop::Corrector(Parser::Source::TreeRewriter)#enforce_policy(event) /Users/mal/parser/lib/parser/source/tree_rewriter.rb:384>,
      @insert_after="",
      @insert_before="",
      @range=#<Parser::Source::Range /Users/mal/rubocop/lib/rubocop/cop/lint/redundant_cop_disable_directive.rb -1...10139>,
      @replacement=nil>,
    @diagnostics=
     #<Parser::Diagnostic::Engine:0x00007fd2803040a8
      @all_errors_are_fatal=false,
      @consumer=#<Proc:0x00007fd280d73b88 /Users/mal/rubocop/lib/rubocop/cop/corrector.rb:26 (lambda)>,
      @ignore_warnings=false>,
    @enforcer=
     #<Method: RuboCop::Cop::Corrector(Parser::Source::TreeRewriter)#enforce_policy(event) /Users/mal/parser/lib/parser/source/tree_rewriter.rb:384>,
    @in_transaction=false,
    @policy={:crossing_deletions=>:accept, :different_replacements=>:raise, :swallowed_insertions=>:raise},
    @source_buffer=
     #<Parser::Source::Buffer:0x00007fd284028358
      @column_for_position=
       {0=>0,
        31=>0,
        102=>0,
        166=>0,
        268=>6,
        343=>6,
        421=>6,
        492=>6,
        571=>6,
        646=>6,
        722=>6,
   #...
    @line_for_position= {
   # ...

Parser::Source::Range has nice inspect and to_s, but Parser::Source::Buffer and Parser::Source::TreeRewriter (at a minimum) would benefit from a summarized version...

I hope to propose a PR one day...