RFR: 8328473: StringTable and SymbolTable statistics delay time to safepoint

[Coleen Phillimore]

This change adds a safepoint poll to gathering statistics for the Symbol and String tables, using the ConcurrentHashTableTasks to chunk up the walk.  The stringTable and symbolTable is similar, like the GrowTask and DeleteTask code.  Maybe this can be cleaned up but I don't have a good idea about that yet that doesn't involve yet another level of templated functions and code. This is already pretty highly templatized.
Tested with tier1-4 and runThese internal test with JFR and failure injection to verify that we do try to safepoint while gathering statistics.

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Commit messages:
 - 8328473: StringTable and SymbolTable statistics delay time to safepoint

Changes: https://git.openjdk.org/jdk/pull/23750/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23750&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8328473
  Stats: 163 lines in 5 files changed: 94 ins; 41 del; 28 mod
  Patch: https://git.openjdk.org/jdk/pull/23750.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23750/head:pull/23750

PR: https://git.openjdk.org/jdk/pull/23750