This change is preparing ground for state update unification for raft bound subsystems. It introduces schema_applier which in the future will become generic interface for applying mutations in raft.
Pulling database::apply() out of schema merging code will allow to batch changes to subsystems. Future generic code will first call prepare() on all implementations, then single database::apply() and then update() on all implementations, then on each shard it will call commit() for all implementations, without preemption so that the change is observed as atomic across all subsystems, and then post_commit().
Backport: no, it's a new feature
Fixes: https://github.com/scylladb/scylladb/issues/19649
Fixes https://github.com/scylladb/scylladb/issues/24531Closesscylladb/scylladb#24886
[avi: adjust for std::vector<mutations> -> utils::chunked_vector<mutations>]
* github.com:scylladb/scylladb:
test: add type creation to test_snapshot
storage_service: always wake up load balancer on update tablet metadata
db: schema_applier: call destroy also when exception occurs
db: replica: simplify seeding ERM during shema change
db: remove cleanup from add_column_family
db: abort on exception during schema commit phase
db: make user defined types changes atomic
replica: db: make keyspace schema changes atomic
db: atomically apply changes to tables and views
replica: make truncate_table_on_all_shards get whole schema from table_shards
service: split update_tablet_metadata into two phases
service: pull out update_tablet_metadata from migration_listener
db: service: add store_service dependency to schema_applier
service: simplify load_tablet_metadata and update_tablet_metadata
db: don't perform move on tablet_hint reference
replica: split add_column_family_and_make_directory into steps
replica: db: split drop_table into steps
db: don't move map references in merge_tables_and_views()
db: introduce commit_on_shard function
db: access types during schema merge via special storage
replica: make non-preemptive keyspace create/update/delete functions public
replica: split update keyspace into two phases
replica: split creating keyspace into two functions
db: rename create_keyspace_from_schema_partition
db: decouple functions and aggregates schema change notification from merging code
db: store functions and aggregates change batch in schema_applier
db: decouple tables and views schema change notifications from merging code
db: store tables and views schema diff in schema_applier
db: decouple user type schema change notifications from types merging code
service: unify keyspace notification functions arguments
db: replica: decouple keyspace schema change notifications to a separate function
db: add class encapsulating schema merging
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