Method constructor

docs/tests/v2/es6/js/sanddance.js:153058–153069

(search, columns)

class Exec {
  constructor(search, columns) {
    this.columns = columns;
    this.groups = VegaDeckGl.util.clone((0, _group.ensureSearchExpressionGroupArray)(search));
    this.groups.forEach(group => {
      group.expressions.forEach(ex => {
        ex.column = this.getColumn(ex.name);
        ex.valueBool = valueToBoolean(ex.value);
        ex.valueLow = valueToString(ex.value).toLocaleLowerCase();
        ex.stringOperation = isStringOperation(ex);
      });
    });
  }

  getColumn(name) {
    for (let i = 0; i < this.columns.length; i++) {