[jdk18u] RFR: 8277072: ObjectStreamClass caches keep ClassLoaders alive

[Roman Kennke]

Hi all,

This pull request contains a backport of commit [8eb453ba](https://github.com/openjdk/jdk/commit/8eb453baebe377697286f7eb32280ca9f1fd7775) from the [openjdk/jdk](https://git.openjdk.java.net/jdk) repository.

The commit being backported was authored by Roman Kennke on 10 Dec 2021 and was reviewed by Roger Riggs and Peter Levart.

It fixes a memory leak in ObjectStreamClass under certain conditions. See bug for details.

Thanks!

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Commit messages:
 - Backport 8eb453baebe377697286f7eb32280ca9f1fd7775

Changes: https://git.openjdk.java.net/jdk18u/pull/36/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk18u&pr=36&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8277072
  Stats: 496 lines in 4 files changed: 284 ins; 186 del; 26 mod
  Patch: https://git.openjdk.java.net/jdk18u/pull/36.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk18u pull/36/head:pull/36

PR: https://git.openjdk.java.net/jdk18u/pull/36