Discovering databases with specific table on a PostgreSQL server
Not in a single query. The information_schema.tables view and the pg_catalog.pg_class table are per-database. You can't query tables across multiple databases in PostgreSQL without hacks like DBLink.

A PostgreSQL database is a bit more like an independent MySQL server, and a PostgreSQL schema is more like a MySQL database. If you want to be able to query across multiple namespaces in PostgreSQL, create them all as schemas within one database, instead of in multiple databases.

To list tables in all databases must connect to each database of interest. You can list them from select * from pg_catalog.pg_database where datistemplate = 'f';. The pg_catalog.pg_database table is global across all databases, so the same results are obtained by connecting to any database.