RFR: 8337876: [IR Framework] Add support for IR tests with @Stable [v3]

[Christian Hagedorn]

> It is currently not possible to write IR tests with `@Stable` annotations because one need to somehow add the IR test classes to the boot classpath. This patch provides support to write such IR tests. I've added a section to the README to provide guidance on how this can be done.
> 
> This is motivated by https://github.com/openjdk/jdk/pull/19635.
> 
> I've tested this patch by taking the current patch of https://github.com/openjdk/jdk/pull/19635, dropping the `RestrictStable` flag and modifying the tests to work with the new IR framework feature:
> 
> TestFramework testFramework = new TestFramework();
> testFramework
>         .addFlags("-XX:-TieredCompilation",
>                   "-XX:+UseParallelGC")
>         .addTestClassesToBootClassPath()
>         .start();
> 
> 
> Thanks,
> Christian

Christian Hagedorn has updated the pull request incrementally with one additional commit since the last revision:

  Fix file separator + add test

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/20477/files
  - new: https://git.openjdk.org/jdk/pull/20477/files/557f9d05..f4ad6df8

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20477&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20477&range=01-02

  Stats: 71 lines in 2 files changed: 70 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20477.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20477/head:pull/20477

PR: https://git.openjdk.org/jdk/pull/20477