RFR: 8252219: C2: Randomize IGVN worklist for stress testing [v5]

[Roberto Castaneda Lozano]

> Add `StressIGVN` option to let C2 randomize IGVN worklist order. When enabled, the worklist is shuffled before each
> main run of the IGVN loop. Also add `GenerateStressSeed` and `StressSeed=N` options to randomly generate or specify the
> seed. In either case, the seed is logged if `LogCompilation` is enabled. The new options are declared as
> production+diagnostic for consistency with the existing `StressLCM` and `StressGCM` options.

Roberto Castaneda Lozano has updated the pull request incrementally with two additional commits since the last revision:

 - Generate random seed if 'StressSeed' is unset
 - Use generic swap() for shuffling

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/242/files
  - new: https://git.openjdk.java.net/jdk/pull/242/files/829b1a1a..91812e58

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=242&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=242&range=03-04

  Stats: 25 lines in 7 files changed: 2 ins; 14 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/242.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/242/head:pull/242

PR: https://git.openjdk.java.net/jdk/pull/242