The low-level `mutation_fragment_stream_validator` gets `reset()` methods that until now only the high-level `mutation_fragment_stream_validating_filter` had.
Active tombstone validation is pushed down to the low level validator.
The low level validator, which was a pain to use until now due to being very fussy on which subset of its API one used, is made much more robust, not requiring the user to stick to a subset of its API anymore.
Closes#11614
* github.com:scylladb/scylladb:
mutation_fragment_stream_validator: make interface more robust
mutation_fragment_stream_validator: add reset() to validating filter
mutation_fragment_stream_validator: move active tomsbtone validation into low level validator
9dae2b9c02