BigQuery: enable FROM-first SELECT

[moshap-firebolt]

BigQuery allows a query to start with FROM, e.g. FROM t and FROM t SELECT *,
which is also the entry form for pipe syntax (FROM t |> ...).

The parser already supports FROM-first SELECT behind
Dialect::supports_from_first_select() (enabled for ClickHouse, DuckDB and
Generic); this enables it for BigQuery as well. The existing
test_select_from_first / test_select_from_first_with_cte, parameterized over
all_dialects_where(|d| d.supports_from_first_select()), now cover BigQuery.

Docs: https://cloud.google.com/bigquery/docs/reference/standard-sql/query-syntax#from_queries

[LucaCappelletti94]

Include tests for the big query dialect to avoid regressions.

[moshap-firebolt]

Include tests for the big query dialect to avoid regressions.

Done.

[iffyio]

Suggested change

	// The bare form has no explicit SELECT and parses as `FromFirstNoSelect`;
	// adding a SELECT switches it to `FromFirst`.
	match bigquery().verified_stmt("FROM t") {
	Statement::Query(query) => match *query.body {
	SetExpr::Select(select) => {
	assert_eq!(select.flavor, SelectFlavor::FromFirstNoSelect)
	}
	other => panic!("expected a select, got {other:?}"),
	},
	other => panic!("expected a query, got {other:?}"),
	}
	match bigquery().verified_stmt("FROM t SELECT a, b") {
	Statement::Query(query) => match *query.body {
	SetExpr::Select(select) => assert_eq!(select.flavor, SelectFlavor::FromFirst),
	other => panic!("expected a select, got {other:?}"),
	},
	other => panic!("expected a query, got {other:?}"),

[iffyio]

Suggested change

	// BigQuery allows a query to begin with `FROM`, both on its own and as the
	// entry form for pipe syntax.