[11u] RFR (S) 8259231: Epsilon: improve performance under contention during virtual space expansion

[Aleksey Shipilev]

Original RFE:
   https://bugs.openjdk.java.net/browse/JDK-8259231
   https://git.openjdk.java.net/jdk/commit/722f2361

The patch would have applied cleanly, if not for MutexLockerEx -> MutexLocker renames in subsequent 
JDKs. So I had to reapply the hunk by hand. The resulting patch differs from the original one only 
in MutexLocker line.

11u variant:
   https://cr.openjdk.java.net/~shade/8259231/webrev.11u.01/

Testing: gc/epsilon {fastdebug,release} x {x86_64,aarch64}

-- 
Thanks,
-Aleksey