RFR: JDK-8314211: Add NativeLibraryUnload event [v2]

[Matthias Baesken]

> [JDK-8313251](https://bugs.openjdk.org/browse/JDK-8313251) introduced a a NativeLibraryLoad event that provides us more detail about shared lib/dll loads.
> There should be a similar event for unload operations of shared libs.

Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:

  Simplify os_windows code

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15272/files
  - new: https://git.openjdk.org/jdk/pull/15272/files/ce607b38..b7557a5d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15272&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15272&range=00-01

  Stats: 5 lines in 1 file changed: 1 ins; 3 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/15272.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15272/head:pull/15272

PR: https://git.openjdk.org/jdk/pull/15272