RFR: 8222986: Add parameter to skip clearing CHeapBitMaps when resizing

[Stefan Karlsson]

Hi all,

Please review this patch to add a 'clear' parameter to the CHeapBitMap 
initialize, resize, and reinitialize functions.

https://cr.openjdk.java.net/~stefank/8222986/webrev.01/
https://bugs.openjdk.java.net/browse/JDK-8222986

We want this functionally for the ZUncommit feature, where we now split 
ZPages and resize the bitmaps. These bitmaps are cleared lazily, so we 
don't want to also clear them when they are resized.

Thanks,
StefanK