JDK 16 RFR of JDK-8235496 : "Start of release updates for JDK 16" and related work

[Joe Darcy]

Hello,

The start of JDK 16 is right around the corner with JDK 15 forking off 
from jdk/jdk at ramp down 1 [1].

Please review the usual hotspot-related portions of

     http://cr.openjdk.java.net/~darcy/8235496.4/

The hotspot src and test updates were as expected; thanks to David H. 
and Mikael V. for early assistance.

Related review threads started on compiler-dev and build-dev.

Thanks,

-Joe

[1] http://openjdk.java.net/projects/jdk/15/