Move to ASM9 / JDK 15 + experimental support of JDK 16
This patch
- rename PermittedSubtypes to PermittedSubclasses per upcoming VM spec
- visitPermittedSubclasses() is not experimental anymore, i've choosen to create a ASM10_EXPERIMENTAL even if there is no experimental feature anymore, it makes the code more clean (ASM9 (latest api) != ASM10_EXPERIMENTAL (latest))
- rename some accidentally overloaded methods to appease CheckStyle
- add ASM9 API
- add support of JDK 16 version (60)
The patch will be squashed before being merged.