toArray() {
    if (!this._sorted) {
      this._array.sort(util.compareByGeneratedPositionsInflated)
      this._sorted = true
    }
    return this._array
  }
Returns the flat, sorted array of mappings. The mappings are sorted by
generated position.

WARNING: This method returns internal data without copying, for
performance. The return value must NOT be mutated, and should be treated as
an immutable borrow. If you want to take ownership, you must make your own
copy.