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

[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

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Commit messages:
 - JDK-8369530: update copyright year
 - JDK-8369530: [lworld] Improve execution time of compiler tests

Changes: https://git.openjdk.org/valhalla/pull/1708/files
  Webrev: https://webrevs.openjdk.org/?repo=valhalla&pr=1708&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369530
  Stats: 959 lines in 12 files changed: 930 ins; 0 del; 29 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