RFR: 8340974: Ambiguous name of jtreg property vm.libgraal.enabled

[Todd V. Jonker]

This disambiguates the situation where libgraal is "enabled" for use by non-CompilerBroker compilations, without being used as the JIT compiler.

Per discussion at https://github.com/openjdk/jdk/pull/21120#issuecomment-2372462365 

Grep shows that the property and related method are not used in this codebase.  Tier1 tests on linux-x86_64-server-release pass cleanly.

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

Commit messages:
 - Rename jtreg property vm.libgraal.enabled to vm.libgraal.jit.

Changes: https://git.openjdk.org/jdk/pull/21190/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=21190&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8340974
  Stats: 4 lines in 2 files changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/21190.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21190/head:pull/21190

PR: https://git.openjdk.org/jdk/pull/21190