RFR: 8311946: add support for libgraal specific jtreg tests [v3]

[Doug Simon]

> This PR adds support for a `vm.libgraal.enabled` property that can be used with the jtreg `@requires` tag to determine if the VM under test is using libgraal as the JIT.

Doug Simon has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains four additional commits since the last revision:

 - add support for vm.libgraal property and fix problems with vm.libgraal.enabled property
 - Merge remote-tracking branch 'openjdk-jdk/master' into JDK-8311946
 - fix wrong flag name
 - add support for vm.libgraal.enabled property

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14851/files
  - new: https://git.openjdk.org/jdk/pull/14851/files/c0cbca79..ce7c1cba

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14851&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14851&range=01-02

  Stats: 10960 lines in 131 files changed: 5120 ins; 5610 del; 230 mod
  Patch: https://git.openjdk.org/jdk/pull/14851.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14851/head:pull/14851

PR: https://git.openjdk.org/jdk/pull/14851