TIMESTAMP_INSTANT should be primitive

Currently TIMESTAMP_INSTANT is defined as a non-primitive type. While TIMESTAMP is a primitive type.

https://github.com/apache/orc/blob/cfa749854fd4fd78c763762f3515f33b9a206072/java/core/src/java/org/apache/orc/TypeDescription.java#L119

TIMESTAMP_INSTANT("timestamp with local time zone", false);
Category(String name, boolean isPrimitive) {
  this.name = name;
  this.isPrimitive = isPrimitive;
}

This can cause problems in code that branches based on type.getCategory().isPrimitive()