RFR: 8252219: C2: Randomize IGVN worklist for stress testing [v4]

[Roberto Castañeda 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 Castañeda Lozano has updated the pull request incrementally with three additional commits since the last
revision:

 - Add basic sanity test for stress IGVN options
 - Fix typo
 - Move shuffle() to PhaseIterGVN

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

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/242/files
  - new: https://git.openjdk.java.net/jdk/pull/242/files/e1131852..829b1a1a

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=242&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=242&range=02-03

  Stats: 74 lines in 7 files changed: 58 ins; 10 del; 6 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