RFR: 8340728: Test vmTestbase/gc/memory/Nio/Nio.java is failing to allocate all direct buffer memory [v3]

[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 incrementally with one additional commit since the last revision:

  8340728: Fail if too much direct memory was allocated before this test is run

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/21623/files
  - new: https://git.openjdk.org/jdk/pull/21623/files/b1e0c4d8..ee76ec14

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21623&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21623&range=01-02

  Stats: 12 lines in 1 file changed: 9 ins; 0 del; 3 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