Rework CompositeProxy and improve test coverage (96%). In the process of adding tests and filling the test coverage gap, it turned out that the implementation was tailored to very specific use cases, and generic tests failed. Reworked the implementation to make it more flexible.
--------- - [x] I confirm that I make this contribution in accordance with the [OpenJDK Interim AI Policy](https://openjdk.org/legal/ai). ------------- Commit messages: - CompositeProxy: Streamline and better coverage (96%). More fleixible dispatching of proxy method calls between input slices - CompositeProxyTest: remove redundancy from testBasicObjectMethods() test - JUnitUtils: add StringArrayConverter class Changes: https://git.openjdk.org/jdk/pull/30675/files Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=30675&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8382022 Stats: 1575 lines in 3 files changed: 1256 ins; 141 del; 178 mod Patch: https://git.openjdk.org/jdk/pull/30675.diff Fetch: git fetch https://git.openjdk.org/jdk.git pull/30675/head:pull/30675 PR: https://git.openjdk.org/jdk/pull/30675
