mutation_reader: move slicing filtering reader into readers/

Only the declaration has to be moved, the definition is already in
readers/mutation_readers.cc.

db/virtual_table.cc

@@ -14,6 +14,7 @@
 #include "db/chained_delegating_reader.hh"
 #include "readers/reversing.hh"
 #include "readers/forwardable.hh"
+#include "readers/slicing_filtering.hh"
 
 namespace db {
 

mutation_reader.hh

@@ -19,9 +19,6 @@
 #include "reader_concurrency_semaphore.hh"
 #include <seastar/core/io_priority_class.hh>
 
-/// Create a wrapper that filters fragments according to partition range and slice.
-flat_mutation_reader make_slicing_filtering_reader(flat_mutation_reader, const dht::partition_range&, const query::partition_slice&);
-
 /// A partition_presence_checker quickly returns whether a key is known not to exist
 /// in a data source (it may return false positives, but not false negatives).
 enum class partition_presence_checker_result {

readers/slicing_filtering.hh

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2022-present ScyllaDB
+ */
+
+/*
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+#pragma once
+
+#include "interval.hh"
+
+class flat_mutation_reader;
+
+namespace dht {
+class ring_position;
+using partition_range = nonwrapping_interval<ring_position>;
+}
+
+namespace query {
+class partition_slice;
+}
+
+/// Create a wrapper that filters fragments according to partition range and slice.
+flat_mutation_reader make_slicing_filtering_reader(flat_mutation_reader, const dht::partition_range&, const query::partition_slice&);