Refactor the core level snapshot cleanup mechanism to rely on Lucene

SOLR-9269 introduced a mechanism to create/delete snapshots for a Solr core (using Lucene IndexDeletionPolicy). The current snapshot cleanup mechanism is based on reference counting the index files shared between multiple segments. Since this mechanism completely skips the Lucene APIs, it is not portable (e.g. it doesn't work on 4.10.3 version).

I propose an alternative implementation which relies exclusively on Lucene IndexWriter (+ IndexDeletionPolicy) for cleanup.