RFR: 8227060: Optimize safepoint cleanup subtask order [v2]

[Coleen Phillimore]

> Most of the analysis in the CR is for code that's removed, but I found one safepoint cleanup task that's unused.  Also the dictionary resizing and symbol/string table rehashing, while rare, could take a long time so I moved them sooner in the list.
> Tested with tier1-3.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Kim's improvement ideas.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/9515/files
  - new: https://git.openjdk.org/jdk/pull/9515/files/6e5786c9..9e49a30b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=9515&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=9515&range=00-01

  Stats: 23 lines in 1 file changed: 8 ins; 9 del; 6 mod
  Patch: https://git.openjdk.org/jdk/pull/9515.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9515/head:pull/9515

PR: https://git.openjdk.org/jdk/pull/9515