typeAheadUp() {
      for (let i = this.typeAheadPointer - 1; i >= 0; i--) {
        if (this.selectable(this.filteredOptions[i])) {
          this.typeAheadPointer = i
          break
        }
      }
    }
Move the typeAheadPointer visually up the list by
setting it to the previous selectable option.
@return {void}