make internal-class-loader indy compatible

[SylvainJuge]

Part of #11457

Migrates the internal/classloader module to be indy-compatible.

Also removes leftover usages of readOnly = false for return values on a few other modules:

• internal/osgi
• internal-reflection (integration tests)
• internal/internal-url-class-loader (integration tests)

[SylvainJuge]

There are a few extra challenges discovered while implementing this:

• the initial migration went well, but did not work for indy 192137a
• I had to work-around a bug when skipOn is used and advices do not return an array d40c2b3
• classloader instrumentation had to be migrated to ASM because it triggered stack overflow or nested invokedynamic invocations (instrument loading classes while loading advices/helper is probably not a very good mix).

[SylvainJuge]

Closing in favor of #12242