Add ClassTweaker support

[thecatcore]

ClassTweaker is the new system that replaces AccessWideners in Fabric Loader 0.18+.

Some notable new features include: Interface Injection

[wagyourtail]

is there an example of this file format somewhere? or a spec or something? I don't really want to figure it out from reading fabric's file parser

[thecatcore]

Example in Fabric API repo