RFR: 8356838: AOT incorrectly sets a cached class's loader type to boot

[Ioi Lam]

When the AOT training run sees a class `X` loaded by a custom class loader, we should set `X`'s loader type to `unreg`. However, since [JDK-8348426](https://bugs.openjdk.org/browse/JDK-8348426), if the classfile for `X` can also be found under the module path, we will incorrectly set the loader type to `boot`. See `test3()` in the new test code.

The fix is to check for custom class loaders in `ClassLoader::record_result()` before checking the `classpath_index`.

I also cleaned up the code in `ClassLoader::record_result()` and `ClassLoaderExt::record_result_for_builtin_loader()` to reduce redundancy and improve readability.

I added `AOTClassLocationConfig::print()` which can be called inside gdb for debugging purposes.

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Commit messages:
 - More clean up
 - added tests
 - Clean up; removed test code
 - step1

Changes: https://git.openjdk.org/jdk/pull/25199/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25199&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356838
  Stats: 147 lines in 8 files changed: 114 ins; 14 del; 19 mod
  Patch: https://git.openjdk.org/jdk/pull/25199.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25199/head:pull/25199

PR: https://git.openjdk.org/jdk/pull/25199