protected int largestLowerBoundSlotFor(ByteBuffer idx, long target, IndexSearchType searchEntity) {
        return indexSlotRangeFor(idx, target, searchEntity, SearchResultType.LARGEST_LOWER_BOUND);
    }
Find the slot in which the largest entry less than or equal to the given target key or value is stored.
The comparison is made using the `IndexEntry.compareTo()` method.

@param idx The index buffer
@param target The index key to look for
@return The slot found or -1 if the least entry in the index is larger than the target key or the index is empty
storage/src/main/java/org/apache/kafka/storage/internals/log/AbstractIndex.java