RFR: 8342376: More reliable OOM handling in ExceptionDuringDumpAtObjectsInitPhase test

[Aleksey Shipilev]

Found a test bug while testing [JDK-8341913](https://bugs.openjdk.org/browse/JDK-8341913) with Shenandoah. For OOM testing, the test fills out the heap with large arrays and then attempts to allocate a smaller array.

That allocation almost always succeeds with Shenandoah. Actually, it succeeds with other GCs as well, it just so happens that other GCs throw OOM with "GC overhead limit exceeded".

Plus, some allocations should be sinked to avoid dead-code elimination.

Additional testing:
 - [x] Linux x86_64 server fastdebug, test now passes reliably with JDK-8341913 and Shenandoah
 - [ ] Linux x86_64 server fastdebug, test with {Serial, Parallel, G1, Shenandoah, Z}, 50 times

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Commit messages:
 - Allocation sizes closer to original
 - Fix

Changes: https://git.openjdk.org/jdk/pull/21536/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21536&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342376
  Stats: 11 lines in 1 file changed: 5 ins; 0 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/21536.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21536/head:pull/21536

PR: https://git.openjdk.org/jdk/pull/21536