RFR: ZGC: Remove abbreviations in JFR events

[Stefan Karlsson]

Hi all,

The following test fails if events have the words stat or alloc in names:
test/jdk/jdk/jfr/event/metadata/TestEventMetadata.java

I've updated the ZGC JFR events to adhere to these strict conventions, 
so that we pass this tests.

http://cr.openjdk.java.net/~stefank/zgc/zJfrMetadata/webrev.01/

StefanK