RFR(S) : 8225554 : add JFR event for uncommon trap

[Igor Ignatyev]

http://cr.openjdk.java.net/~iignatyev//8225554/webrev.00/index.html
> 187 lines changed: 184 ins; 0 del; 3 mod;

Hi all,

could you please review this small patch which adds jfr event for uncommon trap?

webrev: http://cr.openjdk.java.net/~iignatyev//8225554/webrev.00/index.html
JBS: https://bugs.openjdk.java.net/browse/JDK-8225554
testing:
 - tier1 (which includes a newly added test)
 - modified version of compiler/intrinsics/klass/CastNullCheckDroppingsTest.java (see JDK-8129092[1])

[1] https://bugs.openjdk.java.net/browse/JDK-8129092

Thanks,
-- Igor