SourceDefinition.meta should represent merged base meta and table_meta

[MichelleArk]

Housekeeping

• I am a maintainer of dbt-core

Short description

As part of the adapter decoupling work, we removed the BaseRelation.create_from_source and BaseRelation.create_from_node methods in favor of a consolidated BaseRelation.create_from method that accepts quoting: HasQuoting and relation_config: RelationConfig (#9210).

RelationConfig includes meta, as this is a common attribute shared across most node types & sources. However, for adapters that were relying on accessing source_meta to get the source-level metadata (e.g. duckdb), meta is not sufficient because it only includes the table meta, and uses source_meta to store the source-level meta property

Acceptance criteria

In dbt-core, update the meta field on SourceDefinition to include fields from source_meta by default.

This should be a backward compatible change if table_meta takes precedence over source_meta, which would be expected by dbt's typical config handling.

Suggested Tests

1. SourceDefinition parsing should apply the appropriate precedence between table & source meta as described in AC

Impact to Other Teams

None

Will backports be required?

No

Context

Alternative options considered here: duckdb/dbt-duckdb#342 (comment)