chore: Migrate maximum_op operator to SQLGlot

[jialuoo]

Migrated the maximum_op and minimum_op operators to SQLGlot.

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Fixes b/447388852 🦕

[jialuoo]

The sql from ibis:

SELECT
  CASE
    WHEN (
      `t0`.`float64_col` IS NULL
    ) OR (
      `t0`.`int64_col` < `t0`.`float64_col`
    )
    THEN `t0`.`float64_col`
    ELSE `t0`.`int64_col`
  END AS `int64_col`
FROM (
  SELECT
    `int64_col`,
    `float64_col`
  FROM `bigframes-dev.sqlglot_test.scalar_types`
) AS `t0`