Completely mechanical change.
The cache should not garbage-collect tombstone which cover data in the memtable. Add overlap checks (get_max_purgeable) to garbage collection to detect tombstones which cover data in the memtable and to prevent their garbage collection.
As requested in #22097, moved the files and fixed other includes and build system. Fixes: #22097 Signed-off-by: Ran Regev <ran.regev@scylladb.com> Closes scylladb/scylladb#22495