Truffle/Source Attribution: Replace direct creation of SourceSection objects with factory methods on Source; two of these greatly simplify source attribution by automatically computing either the row/column start location from a character offset or vice versa, depending on what?s made available from the parser. Minor API change on Visualizer.

// I can cast any old thing I want to this type object:
public class You_Have_Been_P0wned {
  // Make a bunch of int-fields so I can peek & poke it
  int _a;
  int _b;
  int _c;
  int _d;

}