RFR: 8339341: SurfaceManager cacheMap retains strong references

[Nikita Gubarkov]

I moved SurfaceDataProxy cache into a separate class.
Now caching level is determined by placement of the SurfaceManager.ProxyCache object instead of a "proxy key". This cache "owns" proxies and therefore strong refs via them do not prevent the cache and GraphicsConfig from being detected as weakly reachable.

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Commit messages:
 - 8339341: Make SurfaceDataProxy cache a separate entity.

Changes: https://git.openjdk.org/jdk/pull/20825/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20825&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339341
  Stats: 173 lines in 17 files changed: 55 ins; 55 del; 63 mod
  Patch: https://git.openjdk.org/jdk/pull/20825.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20825/head:pull/20825

PR: https://git.openjdk.org/jdk/pull/20825