Java 9 cleanups compatible with Java 8

This Merge Request aims to update DiSL with backward-compatible changes in order to prepare it to be updated to Java9+.

Here is a list of changes and new implementations that have been done to achieve this goal:

• Updated ASM to the latest version, 7.2.
• Replaced javah, which has been removed in Java 9, with javac -h.
• Implemented codeflags generation introducing @Native annotation.
• Fixed ShadowVM tests: removed ASM specific pseudo access flags not defined in the JVM specification. They can potentially make some tests fail when comparing ShadowField and Field modifiers.
• Updated Google Protobuf (renamed to protobuf-javalite).