Currently no mutation-source supports reading in reverse natively but
we are working on changing that, adding native reverse read support to
memtable, cache and sstable readers. To ensure that all mutation
sources work in a correct and uniform manner when reading in reverse,
we add a reverse test to the mutation source test suite. This test
reverses the data that it passes to `populate()`, then reads in
forward order (in reverse compared to the data order). For this we use
the currently established reverse read API: reverse schema (schema
order == query order) and half-reversed (legacy) slice. All mutation
sources are prepared to work with reversed reads, using the
`make_reversing_reader()` adapter. As we progress with our native
reverse support, we will replace these adapters with native reversing
support. As part of this, we push down the reversing reader adapter
currently existing on the `query::consume_page()` level, to the
individual mutation sources.
Closes#9384
* github.com:scylladb/scylla:
test: mutation_reader_test: reversed version of test_clustering_order_merger_sstable_set
querier: consume_page(): remove now unused max_size parameter
test/lib: mutation_source_test: test reading in reverse
test: mutation_reader_test: clustering_combined_reader_mutation_source_test: prepare for reading in reverse
test: flat_mutation_reader_test: test_reverse_reader_is_mutation_source: prepare for reading in reverse
test: mutation_reader_test: test_manual_paused_evictable_reader_is_mutation_source: use query schema instead of table schema
treewide: move reversing to the mutation sources
mutation_query: reconcilable_result_builder: document reverse query preconditions
sstable_set: time_series_sstable_set: reverse mode
mutlishard_mutation_query: set max result size on used permits
db/virtual_table: streaming_virtual_table::as_mutation_source(): use query schema instead of table schema
flat_mutation_reader: make_reversing_reader(): add convenience stored slice
mutation_reader: evictable_reader: add reverse read support
flat_mutation_reader: make_flat_mutation_reader_from_fragments(): add reverse read support
flat_mutation_reader: flat_mutation_reader_from_mutations(): add reverse read support
flat_mutation_reader: flat_mutation_reader_from_mutations(): document preconditions
query-request: introduce `half_reverse_slice`
flat_mutation_reader_assertions: log what's expected
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