This removes Elasticsearch's filter cache and uses Lucene's instead. It has some
implications:
- custom cache keys (`_cache_key`) are unsupported
- decisions are made internally and can't be overridden by users ('_cache`)
- not only filters can be cached but also all queries that do not need scores
- parent/child queries can now be cached, however cached entries are only
valid for the current top-level reader so in practice it will likely only
be used on read-only indices
- the cache deduplicates filters, which plays nicer with large keys (eg. `terms`)
- better stats: we already had ram usage and evictions, but now also hit count,
miss count, lookup count, number of cached doc id sets and current number of
doc id sets in the cache
- dynamically changing the filter cache size is not supported anymore
Internally, an important change is that it removes the NoCacheFilter infrastructure
in favour of making Query.rewrite specializing the query for the current reader so
that it will only be cached on this reader (look for IndexCacheableQuery).
Note that consuming filters with the query API (createWeight/scorer) instead of
the filter API (getDocIdSet) is important for parent/child queries because
otherwise a QueryWrapperFilter(ParentQuery) would run the wrapped query per
segment while relations might be cross segments.
b72f27a410