_getIndexes(key) {
    const bucketIndex = this.hashFunction(key);
    const values = this.buckets[bucketIndex] || [];

    for (let entryIndex = 0; entryIndex < values.length; entryIndex++) {
      const entry = values[entryIndex];
      if (entry.key === key) {
        return { bucketIndex, entryIndex, keyIndex: entry.keyIndex };
      }
    }

    return { bucketIndex };
  }
Search for a key in the map. It returns it's internal array indexes.
Returns bucketIndex and the internal array index
@param {any} key