RegexpQueryNode inconsistent treatment of begin and end parameters [LUCENE-6498]

[asfimport]

RegexpQueryNode has some questionable treatment of the begin and end parameters:

  public RegexpQueryNode(CharSequence field, CharSequence text, int begin,
      int end) {
    this.field = field;
    this.text = text.subSequence(begin, end);
  }

when contrasted with FieldQueryNode:

  public FieldQueryNode(CharSequence field, CharSequence text, int begin,
      int end) {
    this.field = field;
    this.text = text;
    this.begin = begin;
    this.end = end;
    this.setLeaf(true);
  }

I am now not entirely sure which of the two is correct...

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Migrated from LUCENE-6498 by Trejkaz