RFR: JDK-8205549 JDK-8205698 Support of flattened values in Unsafe

[mandy chung]

On 6/29/18 11:58 AM, mandy chung wrote:
> Revised webrev:
> http://cr.openjdk.java.net/~mchung/valhalla/webrevs/unsafe-flat-fields-webrev.01/ 

Thinking it again, I went with the global lock suggestion.

ValueAcquire/Release/Opaque accessor method calls the ValueVolatile
method which acquire the lock.

I also changed the static fieldValueType/staticFieldValueType to
access the final `fieldType` field directly.

Webrev updated in place.

Mandy