[lworld] RFR: 8369530: [lworld] Improve execution time of compiler tests [v2]

[Damon Fenacci]

> # Issue
> 
> Several Valhalla compiler specific tests are slow and this affects the overall execution time of lower tiers.
> [JDK-8369437](https://bugs.openjdk.org/browse/JDK-8369437) has already improved the situation by splitting multiple @run statements in compiler tests into separate @test blocks for several tests. There are nevertheless still a handful of tests that take up to a dozen minutes to finish.
> 
> # Cause
> 
> Most tests affected are using multiple IR-Framework scenarios to start tests with different flags. The tests are started sequentially, adding the execution time of each test. The problem is similar to [JDK-8369437](https://bugs.openjdk.org/browse/JDK-8369437) but at IR-Framework level.
> 
> # Fix
> 
> We can parallelize the execution of scenarios similar to what has been done in the [fix](https://github.com/openjdk/valhalla/pull/1681/files) for [JDK-8369437](https://bugs.openjdk.org/browse/JDK-8369437). Unfortunately the IR-Framework doesn't allow tests to be run on different machines and there is no simple way to make it interact with JTReg in that way. So, as a provisional and minimalistic solution, scenarios are added and started one by one and run by individual JTReg `@test` entries.
> 
> # Testing
> 
> Tier 1-3
> Worst-time compiler/valhalla JTReg tests went from 16min to <2min

Damon Fenacci has updated the pull request incrementally with one additional commit since the last revision:

  JDK-8369530: remove import

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

Changes:
  - all: https://git.openjdk.org/valhalla/pull/1708/files
  - new: https://git.openjdk.org/valhalla/pull/1708/files/9e4666ac..411f809b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=valhalla&pr=1708&range=01
 - incr: https://webrevs.openjdk.org/?repo=valhalla&pr=1708&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/valhalla/pull/1708.diff
  Fetch: git fetch https://git.openjdk.org/valhalla.git pull/1708/head:pull/1708

PR: https://git.openjdk.org/valhalla/pull/1708