RFR: 8348610: GenShen: TestShenandoahEvacuationInformationEvent failed with setRegions >= regionsFreed: expected 1 >= 57

[Satyen Subramaniam]

Renaming `ShenandoahEvacuationInformation.freedRegions` to `ShenandoahEvacuationInformation.freeRegions` for clarity, and fixing incorrect assertion in  TestShenandoahEvacuationInformationEvent.cpp

Tested with tier 1, tier 2, and tier 3 tests.

-------------

Commit messages:
 - Adjusting ShenandoahEvacuationInformation event and test assertions

Changes: https://git.openjdk.org/shenandoah/pull/558/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=558&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348610
  Stats: 14 lines in 5 files changed: 2 ins; 1 del; 11 mod
  Patch: https://git.openjdk.org/shenandoah/pull/558.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/558/head:pull/558

PR: https://git.openjdk.org/shenandoah/pull/558