RFR: 8309697: [TESTBUG] Remove "@requires vm.flagless" from jtreg vectorization tests [v4]

[Pengfei Li]

> This patch removes `@require vm.flagless` annotations from HotSpot jtreg tests in `compiler/vectorization/runner`. All jtreg cases in this folder are invoked by test driver `VectorizationTestRunner.java` which checks both correctness and vectorizability (IR) for each test method. We added flagless requirement before because extra flags may mess with compiler control in the test driver for correctness check. But `flagless` has a side effect that it makes tests with extra flags skipped. So we propose to get rid of it now.
> 
> To adapt the removal of `@require vm.flagless`, a few checks are added in the test driver to skip the correctness check if extra flags make the compiler control not work. This patch also moves previously hard-coded flag `-XX:-OptimizeFill` in the test driver to conditions in IR checks.
> 
> Tested various of compiler control related VM flags on x86 and AArch64.

Pengfei Li has updated the pull request incrementally with one additional commit since the last revision:

  Remove useless conditions and imports

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15011/files
  - new: https://git.openjdk.org/jdk/pull/15011/files/5bb67000..00d48cc8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15011&range=03
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15011&range=02-03

  Stats: 27 lines in 1 file changed: 3 ins; 19 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/15011.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15011/head:pull/15011

PR: https://git.openjdk.org/jdk/pull/15011