Add support for single line comments.

[tacosontitan]

Single-line comments in JSON are defined in the same way they are in JavaScript:

fragment Single_Line_Comment
    : '//' Input_Character*
    ;

fragment Input_Character
    // anything but New_Line_Character
    : ~('\u000D' | '\u000A'   | '\u0085' | '\u2028' | '\u2029')
    ;
    
fragment New_Line_Character
    : '\u000D'  // carriage return
    | '\u000A'  // line feed
    | '\u0085'  // next line
    | '\u2028'  // line separator
    | '\u2029'  // paragraph separator
    ;

_{👆🏻 multiline comment lexical structure excluded.}

This issue requests the addition of support for single-line comments to the JSON library even though they aren't an official part of the spec. Many developers still add comments to JSON files and the JsonLexer could simply discard those, but that's likely a better decision for the consumer to make instead.

Acceptance Criteria

• JsonLexer returns CommentToken for single-line comments.
• Column number advances when horizontal movement is captured.
• Line number advances when vertical movement is captured.
  • Column number is reset to 0 when line number advances.
• Captured comments exclude whitespace.
  • 👆🏻 this should be configurable.
• Test coverage for implementation.