[jdk16] RFR: 8258007: Add instrumentation to NativeLibraryTest [v3]

[Brent Christian]

> This change adds some extra test output for NativeLibraryTest, primarily via an update to the ForceGC utility class.
> 
> It was observed that there was nothing preventing the Cleaner from cleaning the short-lived Object that ForceGC registers before await()/doit()/System.gc() is even called.
> 
> The new 'o' reference is kept alive until FoceGC.await() has been called.
> 
> We should find out a little more the next time NativeLibraryTest fails (or perhaps it won't fail anymore!)

Brent Christian has updated the pull request incrementally with one additional commit since the last revision:

  format() -> println()

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Changes:
  - all: https://git.openjdk.java.net/jdk16/pull/53/files
  - new: https://git.openjdk.java.net/jdk16/pull/53/files/54a9e6d1..f0dd43ae

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk16&pr=53&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk16&pr=53&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk16/pull/53.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk16 pull/53/head:pull/53

PR: https://git.openjdk.java.net/jdk16/pull/53