[13] RFR (T): 8217919: C2: Enable -XX:+AggressiveUnboxing by default

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8217919/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8217919

Once JDK-8217918 [1] is fixed, I propose to enable 
-XX:+AggressiveUnboxing by default.

The optimization noticeably improves EA for primitive boxes (e.g., 
JDK-8055340 [2]), so it's worth having it turned on. It'll also ensure 
the code won't rot again.

Testing: hs-precheckin-comp, tier1-5

Best regards,
Vladimir Ivanov

[1] https://bugs.openjdk.java.net/browse/JDK-8217918
[2] https://bugs.openjdk.java.net/browse/JDK-8055340