[sh/jdk8u] RFR 8269661: JNI_GetStringCritical does not lock char array

[Zhengyu Gu]

This is the bug that only impacts Shenandoah GC, as it is the only GC 
supports object pinning and string deduplication.

Original bug: https://bugs.openjdk.java.net/browse/JDK-8269661
Original patch: 
https://github.com/openjdk/jdk17/commit/0f4e07b7d9190dd44b2fd65eff58fb6ec983a467

The sh/jdk8u backport this based on jdk11u backport patch:
https://github.com/openjdk/jdk11u-dev/commit/2a3d9080e19282f8451cdb93e3e36191f622ea3c

sh/8u webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/JDK-8269661-8u/webrev.00/


The patch diverges from 11u due to that 8u does not support CompactStrings.

Test:
   hotspot_gc_shenandoah


Thanks,

-Zhengyu