RFR 8199868: Support JNI critical functions in object pinning API

[Zhengyu Gu]

Please review this patch that adds JNI critical native support to object 
pinning.

Shenandoah does not block GC while JNI critical session is in progress. 
This patch allows it to pin all incoming array objects before critical 
native call, and unpin them after call completes.


Bug: https://bugs.openjdk.java.net/browse/JDK-8199868
Webrev: http://cr.openjdk.java.net/~zgu/8199868/webrev.00/

Test:

  hotspot_runtime and hotspot_compiler on Linux x86 (fastdebug and release).

Submit test also clean:
   Mach5 mach5-one-zgu-JDK-8199868-20180404-1334-17314: Builds PASSED. 
Testing SUCCESSFUL.


Thanks,

-Zhengyu