RFR: 8311946: add support for libgraal specific jtreg tests [v2]

[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 incrementally with one additional commit since the last revision:

  fix wrong flag name

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Changes:
  - all: https://git.openjdk.org/jdk/pull/14851/files
  - new: https://git.openjdk.org/jdk/pull/14851/files/38d29d35..c0cbca79

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14851&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14851&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 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