RFR: 8272609: Add string deduplication support to SerialGC [v9]

[Denghui Dong]

> Hi team,
> 
> Please help review this change to add string deduplication support to SerialGC.
> 
> Thanks,
> Denghui

Denghui Dong has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains ten commits:

 - Merge branch 'master' into JDK-8272609
 - tidy
 - fix build problem
 - tidy
 - fix build error
 - fix build problem
 - avoid non-local variables with non-trivial / not-constexpr constructors or destructors
 - fix
 - 8272609: Add string deduplication support to SerialGC

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Changes: https://git.openjdk.java.net/jdk/pull/5153/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5153&range=08
  Stats: 248 lines in 19 files changed: 245 ins; 0 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5153.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5153/head:pull/5153

PR: https://git.openjdk.java.net/jdk/pull/5153