Provide safe default implementation of getTableHandle

[findepi]

Provide safe default implementation of
ConnectorMetadata.getTableHandle. This prevents exception when trying
to access a table from a connector that exposes no regular tables at
all, such as GlobalSystemConnector that powers the builtin system
catalog.

This change impacts regular queries for non-existent tables in existing
schemas of the system catalog, such as:

SELECT * FROM system.jdbc.columnxx

After the change, a correct "Table does not exist" error is returned.

This change also affects metadata listing operations, such as

select * from system.jdbc.columns
where table_schem = 'tiny' and table_name = 'nation';

or

select * from system.information_schema.columns
where table_schema = 'jdbc' and table_name = 'columnxx';

Metadata listing operations are highly optimized and call
getTableHandle directly if it is possible to avoid listing tables.
Before the change the query would succeed, but would result in a
ConnectorMetadata getTableHandle() is not implemented exception logged
at WARN level. After the change, no exception is logged.

• fixes ConnectorMetadata getTableHandle() is not implemented exception logged when handling legitimate user query #27045

Release notes

* Return correct "Table does not exist" error when querying a non-existent table in an existing schema within `system` catalog.
* Avoid logging an exception when listing columns from tables from a set of catalogs that includes the `system` catalog. (#27045)

Summary by Sourcery

Provide a safe default implementation of ConnectorMetadata.getTableHandle, fix error handling for non-existent tables in system catalogs, and add tests to verify the correct "Table does not exist" behavior.

Bug Fixes:

• Return a proper "Table does not exist" error instead of throwing exceptions for queries against non-existent tables in system catalogs
• Prevent warning-level exceptions when listing metadata for non-existent tables

Enhancements:

• Add default ConnectorMetadata.getTableHandle method that returns null when a schema has no tables

Tests:

• Add tests for querying non-existent tables in system.metadata and system.runtime connectors to verify error handling