The original implementation of UMIN/UMAX reductions in JDK-8346174
used incorrect identity values in the Java fallback implementation
and test code.

Problem:
--------
UMIN was using MAX_OR_INF (signed maximum value) as the identity:
  - Byte.MAX_VALUE (127) instead of max unsigned byte (255)
  - Short.MAX_VALUE (32767) instead of max unsigned short (65535)
  - Integer.MAX_VALUE instead of max unsigned int (-1)
  - Long.MAX_VALUE instead of max unsigned long (-1)

UMAX was using MIN_OR_INF (signed minimum value) as the identity:
  - Byte.MIN_VALUE (-128) instead of 0
  - Short.MIN_VALUE (-32768) instead of 0
  - Integer.MIN_VALUE instead of 0
  - Long.MIN_VALUE instead of 0

This caused incorrect result. For example:
  UMAX([42,42,...,42]) returned 128 instead of 42