Introduce type alias for Sql[ZResultSet]

[jdegoes]

The type Sql[ZResultSet] is of special significance: it indicates a fragment of a SQL query, which has probably not yet been completed (to represent fully-formed SQL), nor mapped into any concrete data type.

To better indicate the purpose of this type, we can introduce a SqlFragment type alias inside the jdbc package object.

package zio

package object jdbc {
   type SqlFragment = Sql[ZResultSet]
}

Then we can update existing references to Sql[ZResultSet] to instead refer to SqlFragment.

[yisraelU]

@jdegoes I think this can be closed