6173675: M&M: approximate memory allocation rate/amount per thread
Summary: Subclass com.sun.management.ThreadMXBean from java.lang.management.ThreadMXBean, add getAllocatedBytes() and friends to c.s.m.ThreadMXBean and have sun.management.ThreadImpl implement c.s.m.ThreadMXBean rather than j.l.m.ThreadMXBean.
Reviewed-by: mchung, alanb, dholmes, emcmanus