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.