RFR: 8340728: Test vmTestbase/gc/memory/Nio/Nio.java is failing to allocate all direct buffer memory

[Brian Burkhalter]

First attempt to allocate `VM.maxDirectMemory()` bytes of direct buffer memory, decreasing by 1024 bytes for each `OutOfMemoryError` until allocation succeeds.

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Commit messages:
 - 8340728: Test vmTestbase/gc/memory/Nio/Nio.java is failing to allocate all direct buffer memory

Changes: https://git.openjdk.org/jdk/pull/21623/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21623&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340728
  Stats: 25 lines in 2 files changed: 10 ins; 1 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/21623.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21623/head:pull/21623

PR: https://git.openjdk.org/jdk/pull/21623