Most of the machinery was already implemented since it was used when
jumping between clustering ranges of a query slice. We need only perform
one additional thing when performing an index skip during
fast-forwarding: reset the stored range tombstone in the consumer (which
may only be stored in fast-forwarding mode, so it didn't matter that it
wasn't reset earlier). Comments were added to explain the details.
As a preparation for the change, we extend the sstable reversing reader
random schema test with a fast-forwarding test and include some minor
fixes.
Fixes#9427.
Closes#9484
* github.com:scylladb/scylla:
query-request: add comment about clustering ranges with non-full prefix key bounds
sstables: mx: enable position fast-forwarding in reverse mode
test: sstable_conforms_to_mutation_source_test: extend `test_sstable_reversing_reader_random_schema` with fast-forwarding
test: sstable_conforms_to_mutation_source_test: fix `vector::erase` call
test: mutation_source_test: extract `forwardable_reader_to_mutation` function
test: random_schema: fix clustering column printing in `random_schema::cql`
3226c5bf9d