Support user defined precision for numeric columns

Similarly to #1053 it would be nice to be able to specify precision for numeric columns also. Mostly the use case is that without being able to specify our table completely in Exposed then we cannot use the Schema tools for diffing the db table and our `Table` objects in Kotlin.

https://www.w3resource.com/sql/data-type.php#NUMERIC
https://mariadb.com/kb/en/numeric-data-type-overview/