[#21899][#19715] docdb: Move some heartbeat code out of catalog_manag…

…er.cc

Summary:
This diff moves some heartbeat code out of catalog_manager.cc into `master_heartbeat_service.cc`, which is the entry point for the `TsHeartbeat` RPC. This makes it easier to follow the main heartbeat code and makes CatalogManager smaller.
Jira: DB-10798, DB-8520

Test Plan: Existing tests

Reviewers: zdrudi, hsunder

Reviewed By: zdrudi

Subscribers: ybase, bogdan

Differential Revision: https://phorge.dev.yugabyte.com/D33966

src/yb/master/catalog_entity_info.h

@@ -243,6 +243,8 @@ class TabletInfo : public RefCountedThreadSafe<TabletInfo>,
   // Accessors for the latest known tablet replica locations.
   // These locations include only the members of the latest-reported Raft
   // configuration whose tablet servers have ever heartbeated to this Master.
+  // TODO: Make Set/Update private so users are forced to use the catalog manager wrappers which
+  // update the tablet locations version.
   void SetReplicaLocations(std::shared_ptr<TabletReplicaMap> replica_locations);
   std::shared_ptr<const TabletReplicaMap> GetReplicaLocations() const;
   Result<TSDescriptor*> GetLeader() const;