[ORACLE] Wrong JDBC type returned for `current_timestamp`

[DavideD]

Reproducer for OracleColumnDescriptorTest:

  @Test
  public void testMetadata(TestContext ctx) {
    pool.withConnection(conn -> conn.query("SELECT id, val, current_timestamp FROM mutable").execute(), ctx.asyncAssertSuccess(rows -> {
      ...
      // It will return JDBCType.OTHER instead of the expected one
      ctx.assertEquals( JDBCType.TIMESTAMP_WITH_TIMEZONE, rows.columnDescriptors().get(2).jdbcType());
    }));
  }

Note that the typeName() is actually correct.

I've updated the existing testcase here: DavideD@8ddd42b