[sedax90]

Follows #3902. Rebuilt on main on top of the connection's owner of its other databases.

Summary

• A query tab that moves to another database, from the bar or with a USE, asks the window for that database's session. Where a connection's catalog holds only its own database (PostgreSQL, SQL Server), the window opens it beside the connection through OtherDatabases, once for all the tabs asking.
• The tab's completion reads that session's catalog. The tab's own editor session moves as before.
• When a database's session joins, every query tab of the connection in that database reads its catalog, tabs moved while it opened included.
• A statement that changes the catalog in a moved tab refreshes the session that holds that database, the connection's own included.
• A tab restored in another database asks for its session too, once it is in its workspace.
• Completion drops the last database's catalog the moment the tab moves, and ignores a session opened late for a database the tab left.
• Not here: a tab of another database's own workspace keeps that database's catalog when it moves, since the connection's session may not know the name of its own default database.
• Engines whose connection lists every database already (MySQL, ClickHouse, Cassandra, MongoDB) open nothing.

Test plan

• session_window::tests::other_databases::tabs_moved_to_another_database_read_its_session, a_tab_moved_where_the_catalog_lists_every_database_opens_nothing.
• editor::tests::completion_reads_only_the_session_of_the_tabs_database.
• The restored tab's follow and the refresh have no test of their own.
• CI builds and runs the suites. No local Linux runner was available.