pick from master #36316 expression cast( xx as decimal )'s datatype maybe decimalv3 or decimalv2 depending on enable_decimal_conversion value in fe conf file. if enable_decimal_conversion is true, the datatype is decimalv3(9, 0), but the datatype was decimalv3(38, 9) in 2.0 releases. So this pr change the datatype same as 2.0 releases to keep the behavior consistent.