BigQuery: support CREATE VECTOR INDEX

[moshap-firebolt]

BigQuery can create a vector index for approximate nearest-neighbor search over
an embedding column:

CREATE [OR REPLACE] VECTOR INDEX [IF NOT EXISTS] <name>
ON <table>(<column>)
OPTIONS(index_type = 'IVF', distance_type = 'COSINE', ...)

VECTOR is not a keyword, so parse_create previously failed with
Expected: an object type after CREATE, found: VECTOR.

Changes

• Add vector, or_replace and options fields to CreateIndex. VECTOR is
  a modifier on CREATE INDEX (like EXTERNAL on CREATE TABLE), so it reuses
  the existing node rather than a new statement variant. Display renders
  CREATE [OR REPLACE ]VECTOR INDEX ... plus a trailing OPTIONS(...).
• Parse the form in parse_create via a small parse_create_vector_index
  helper; the OPTIONS(...) clause reuses parse_options / SqlOption, so it
  parses and renders the same way as CREATE TABLE / CREATE VIEW OPTIONS.
• Plain CREATE INDEX is unchanged (all three fields default to false/empty).
• New test parse_bigquery_create_vector_index in tests/sqlparser_bigquery.rs
  verifies the round-trip and covers OR REPLACE, IF NOT EXISTS, multi-part
  names and the OPTIONS-less form.

Docs: https://cloud.google.com/bigquery/docs/reference/standard-sql/data-definition-language#create_vector_index_statement