RFR: 8309136: [JVMCI] add -XX:+UseGraalJIT flag [v2]

[Doug Simon]

> Use of the Graal-based JIT in OpenJDK currently requires the following flag: `-XX:+EnableJVMCIProduct`
> 
> This has no direct association with Graal. If the JDK image happens to include a non-Graal JVMCI implementation, it will be automatically selected. This would come as a surprise to users who equate JVMCI with Graal.
> 
> This PR introduces a new flag, `-XX:+UseGraalJIT` to address these shortcomings. The VM fails fast at startup if there is a non-Graal JVMCI implementation or no JVMCI implementation in the JDK image.

Doug Simon has updated the pull request incrementally with one additional commit since the last revision:

  review based fixes

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/14231/files
  - new: https://git.openjdk.org/jdk/pull/14231/files/f9b3538d..235075c1

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=14231&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=14231&range=00-01

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/14231.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/14231/head:pull/14231

PR: https://git.openjdk.org/jdk/pull/14231