RFR: 8340728: Test vmTestbase/gc/memory/Nio/Nio.java is failing to allocate all direct buffer memory [v2]

[Brian Burkhalter]

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

Brian Burkhalter has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains two additional commits since the last revision:

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

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21623/files
  - new: https://git.openjdk.org/jdk/pull/21623/files/6c94f2a6..b1e0c4d8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21623&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21623&range=00-01

  Stats: 113505 lines in 767 files changed: 105030 ins; 5971 del; 2504 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