RFR: 8339366: [jittester] Make it possible to generate tests without execution

[Evgeny Nikitin]

This PR:

1. Extracts IR tree generation from execution (left in the Automatic) into a dedicated class IRTreeGenerator;
2. Introduces a generation result record (named IRTreeGenerator.Test). The record contains main and private classes along with the random seed used for their generation;
3. Creates CLI-wrapper classes for Java and ByteCode generators to allow generation-only execution;
4. Add a repeating option to the configuration - to make it possible to specify several main class names.

Sample usage:

java -cp build/classes --add-opens java.base/java.util=ALL-UNNAMED \
      jdk.test.lib.jittester.JavaCodeGenerator \
      -k Test_0 -k Test_1 -k Test_10

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Commit messages:
 - 8339366: [jittester] Make it possible to generate tests without execution

Changes: https://git.openjdk.org/jdk/pull/20806/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20806&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339366
  Stats: 247 lines in 7 files changed: 167 ins; 59 del; 21 mod
  Patch: https://git.openjdk.org/jdk/pull/20806.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20806/head:pull/20806

PR: https://git.openjdk.org/jdk/pull/20806