Allows searching on number field types (long, short, int, float, double, byte, half_float) when those fields are not
indexed (index: false) but just doc values are enabled.
This enables searches on archive data, which has access to doc values but not index structures. When combined with
searchable snapshots, it allows downloading only data for a given (doc value) field to quickly filter down to a select set
of documents.
Note to reviewers:
I have split isSearchable into two separate methods isIndexed and isSearchable on MappedFieldType. The former one is
about whether actual indexing data structures have been used (postings or points), and the latter one on whether you
can run queries on the given field (e.g. used by field caps). For number field types, queries are now allowed whenever
points are available or when doc values are available (i.e. searchability is expanded).
Relates #81210 and #52728
e421477ac8