Sync Snowflake `VARIANT` type as new `:type/SnowflakeVariant` (#45674)

modules/drivers/snowflake/src/metabase/driver/snowflake.clj

...drivers/snowflake/test/metabase/driver/snowflake_test.clj

src/metabase/lib/convert.cljc

src/metabase/lib/core.cljc

src/metabase/lib/expression.cljc

src/metabase/lib/schema/expression/string.cljc

src/metabase/types.cljc

test/metabase/lib/expression_test.cljc

test/metabase/sync/analyze/fingerprint_test.clj