Databricks: support INSERT BY NAME

[finchxxia]

Summary

This PR adds support for Databricks INSERT ... BY NAME syntax.

• Adds a by_name field to the Insert AST node.
• Parses BY NAME for the Databricks and Generic dialects.
• Preserves BY NAME when formatting the AST back to SQL.
• Adds test coverage for INSERT INTO ... BY NAME with both SELECT and WITH queries.
• Updates existing Insert AST construction sites with the default by_name: false.

Examples

INSERT INTO target BY NAME
SELECT 1 AS a;

INSERT INTO TABLE target BY NAME
WITH source AS (
    SELECT 1 AS event_data_id
)
SELECT event_data_id FROM source;

Testing

cargo test --test sqlparser_databricks test_databricks_insert_by_name
Relevant PostgreSQL INSERT regression tests

[iffyio]

Suggested change

	by_name = columns.is_empty()
	&& self.dialect.supports_insert_by_name()
	by_name = by_name.is_none()
	&& self.dialect.supports_insert_by_name()

I think we can drop the columns check? its not clear why it would be needed at this layer, if the implication is something semantic then that can be left up to the consumer to validate. Relatedly, I assume we need to only set the name if we don't already have one (can we cover that scenario in the tests)?

[finchxxia]

Hi @iffyio , I have committed some changes as per your suggestions. Could you plz take a look again?