findMerges
open override fun findMerges(mergeTrigger: MergeTrigger?, infos: SegmentInfos?, mergeContext: MergePolicy.MergeContext?): MergePolicy.MergeSpecification?
Checks if any merges are now necessary and returns a MergePolicy.MergeSpecification if so. A merge is necessary when there are more than .setMergeFactor segments at a given level. When multiple levels have too many segments, this method will return multiple merges, allowing the MergeScheduler to use concurrency.