Schema.newType() does not validate open content correctly for ISL 2.0

[popematt]

A type constructed with newType() should have the same user_reserved_fields validation as the schema that it is derived from.

@Test
fun gh_issue_232_repro() {
    val iss = IonSchemaSystemBuilder.standard().build()
    val schema = iss.newSchema("\$ion_schema_2_0 type::{ name: foo, type: int }")
    assertThrows<InvalidSchemaException> { schema.newType("type::{ name: bar, description: baz }") }
}

[popematt]

This was fixed serendipitously as part of #238. The only action required is to add the repro test case as a regression test.