format: expose functions/procedures in catalog metadata

### What feature or improvement would you like to see?

Add a `GetObjectsFunctions` and related functions to show user-defined and system functions, aggregate functions, table-valued functions, and stored procedures.

## Prior Art

- [JDBC: getSystemFunctions](https://docs.oracle.com/javase/8/docs/api/java/sql/DatabaseMetaData.html#getSystemFunctions--)
- [JDBC: getFunctions](https://docs.oracle.com/javase/8/docs/api/java/sql/DatabaseMetaData.html#getFunctions-java.lang.String-java.lang.String-java.lang.String-)
- [JDBC: getFunctionColumns](https://docs.oracle.com/javase/8/docs/api/java/sql/DatabaseMetaData.html#getFunctionColumns-java.lang.String-java.lang.String-java.lang.String-java.lang.String-)
- [JDBC: getProcedures](https://docs.oracle.com/javase/8/docs/api/java/sql/DatabaseMetaData.html#getProcedures-java.lang.String-java.lang.String-java.lang.String-)
- [JDBC: getProcedureColumns](https://docs.oracle.com/javase/8/docs/api/java/sql/DatabaseMetaData.html#getProcedureColumns-java.lang.String-java.lang.String-java.lang.String-java.lang.String-)
- [ODBC: SQLProcedures](https://learn.microsoft.com/en-us/sql/odbc/reference/syntax/sqlprocedures-function)
- [ODBC: SQLProcedureColumns()](https://learn.microsoft.com/en-us/sql/odbc/reference/syntax/sqlprocedurecolumns-function)
- BigQuery: https://github.com/adbc-drivers/bigquery/issues/118
- Databricks: https://github.com/adbc-drivers/databricks/issues/236
- PostgreSQL: https://github.com/apache/arrow-adbc/issues/3971
- Snowflake: https://github.com/adbc-drivers/snowflake/issues/77
- Trino: https://github.com/adbc-drivers/trino/issues/60

## Design Issues
- Do we expose system functions, etc. in the same function?
- Do we expose procedures in the same function?
- How do we expose signatures?
- How do we expose overloads?
- How do we provide Arrow-equivalent signatures?
- How do we handle database-specific properties?

## Proposal

TBD

Start by comparing the JDBC and ODBC metadata APIs listed in Prior Art, then review the design questions about system functions, procedures, signatures, overloads, and database-specific properties. There are no implementation files or tests named, and the proposal is TBD; done requires an agreed catalog-metadata API and its scope.

Written by the indexing model from the issue text.