treewide: don't include "db/system_distributed_keyspace.hh" from headers

This just causes unneeded and slower recompliations. Instead replace
with forward declarations, or includes of smaller headers that were
incidentally brought in by the one removed. The .cc files that really
need it gain the include, but they are few.

Ref #1.

Closes #8403

db/view/view.cc

@@ -61,6 +61,7 @@
 #include "db/view/view_updating_consumer.hh"
 #include "db/system_keyspace_view_types.hh"
 #include "db/system_keyspace.hh"
+#include "db/system_distributed_keyspace.hh"
 #include "frozen_mutation.hh"
 #include "gms/inet_address.hh"
 #include "keys.hh"

db/view/view_builder.hh

@@ -22,7 +22,6 @@
 #pragma once
 
 #include "database.hh"
-#include "db/system_distributed_keyspace.hh"
 #include "dht/i_partitioner.hh"
 #include "keys.hh"
 #include "query-request.hh"
@@ -44,6 +43,12 @@
 #include <unordered_map>
 #include <vector>
 
+namespace db {
+
+class system_distributed_keyspace;
+
+}
+
 namespace db::system_keyspace {
 
 using view_name = std::pair<sstring, sstring>;

db/view/view_update_checks.hh

@@ -21,11 +21,16 @@
 
 #pragma once
 
-#include "db/system_distributed_keyspace.hh"
 #include "streaming/stream_reason.hh"
 #include <boost/range/adaptor/map.hpp>
 #include <boost/algorithm/cxx11/any_of.hpp>
 
+namespace db {
+
+class system_distributed_keyspace;
+
+}
+
 namespace db::view {
 
 future<bool> check_view_build_ongoing(db::system_distributed_keyspace& sys_dist_ks, const sstring& ks_name, const sstring& cf_name);