RFR: 8253646: ZGC: Avoid overhead of sorting ZStatIterableValues on bootstrap

[Claes Redestad]

- Defer sorting to when starting the ZStat thread
- Improve the sorting logic to avoid unnecessary strcmps
- Only sort those ZStat objects that actually needs to be sorted

This reduces bootstrap overhead due sorting from around 75k to around 29k instructions when ZStat service is started,
and removes it almost completely otherwise.

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Commit messages:
 - 8253646: ZGC: Avoid overhead of sorting ZStatIterableValues on bootstrap
 - Add missing declaration of sort
 - Sort in-place when starting the ZStat service
 - Missing ResourceMark
 - Fix definition of sampler_cmp
 - Revert experimental shuffling
 - Sort only on print
 - Experiment v2
 - Experiment: Descending alphabetic order should lead to fewer comparisons since we will insert earlier
 - Cleanup and simplify
 - ... and 4 more: https://git.openjdk.java.net/jdk/compare/840aa2b7...43a95a4b

Changes: https://git.openjdk.java.net/jdk/pull/373/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=373&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253646
  Stats: 34 lines in 2 files changed: 21 ins; 4 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/373.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/373/head:pull/373

PR: https://git.openjdk.java.net/jdk/pull/373