Snowflake: Support named file format lifecycle syntax

[osipovartem]

Summary

Add Snowflake parser and AST support for the named file format lifecycle:

ALTER FILE FORMAT IF EXISTS analytics.raw.csv_format SET FIELD_DELIMITER='|';
ALTER FILE FORMAT analytics.raw.csv_format RENAME TO archived_format;
SHOW FILE FORMATS LIKE 'csv%' IN SCHEMA analytics.raw;
DESCRIBE FILE FORMAT analytics.raw.csv_format;
DROP FILE FORMAT IF EXISTS analytics.raw.csv_format;

The syntax is gated by a dialect capability, so other dialects keep their existing behavior. Unsupported SHOW modifiers and empty ALTER SET clauses are rejected instead of being lost during AST round-trip.

Validation

• cargo test --all-features
• cargo fmt --all
• cargo clippy --all-targets --all-features -- -D warnings