fix: initialize the indy dispatcher without Unsafe on modern JDKs

[mvanhorn]

What does this PR do?

On Java 9+, define the java.lang.IndyBootstrapDispatcher resource with Byte Buddy's ClassInjector.UsingLookup: open java.base/java.lang to the agent's actual defining class loader through the existing ElasticApmAgent.openModule API, obtain a private lookup anchored on Object.class, and inject the existing bytes. Keep the Java 7/8 Unsafe path, invoke the newer lookup API reflectively to preserve the Java 7 production API baseline, and retain the initial Class.forName(..., false, null) check so repeated initialization reuses the bootstrap class. Update the production call sites inside IndyBootstrap.java to distinguish the dispatcher lookup anchor from the legacy ModuleSetter injection, and apply the existing J9 module override only when the dispatcher is not already in java.base, comparing modules with Byte Buddy's existing JavaModule abstraction.

On JDK 26+, agent startup can fail while preparing instrumentation because Byte Buddy disables its Unsafe class injector by default. The supplied stack trace reaches IndyBootstrap.loadClassInBootstrap, which still unconditionally uses ClassInjector.UsingUnsafe.ofBootLoader() in this checkout. The maintainer identifies this injection site and suggests method-handle-based injection; -Dnet.bytebuddy.safe=false is a temporary workaround. The June 30 comment says Java 26 was outside the supported-version policy at that time, but neither claims the work nor rejects the proposed code correction.

Fixes #4519

Checklist

• This is an enhancement of existing features, or a new feature in existing plugins
  • I have added tests that prove my fix is effective or that my feature works
  • I have made corresponding changes to the documentation
• This is a bugfix
  • I have added tests that would fail without this fix
• This is a new plugin
  • My code follows the style guidelines of this project
  • I have made corresponding changes to the documentation
  • I have added tests that prove my fix is effective or that my feature works
  • New and existing unit tests pass locally with my changes
• This is something else

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