Change bytecode format for field access to encode field index directly

- class generation context maintains a list of all fields, including fields of the superclass
- therefore, the parser now needs to know exactly the fields of Object and Class to generate the proper information. It is currently hardcoded to avoid further complexity
- disassembler is adapted as well

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Remove escape char to make it easier to grep for error message

Signed-off-by: Stefan Marr <git@stefan-marr.de>
Fix disassembler issue with block

TODO: check whether the block should not have the class as holder
Signed-off-by: Stefan Marr <git@stefan-marr.de>