Add RemapperPreprocessor

Used to "preprocess" a class file, using the ASM tree API,
before remapping with JarRemapper. Right now it only
extracts the inheritance and adds to an InheritanceMap.

Code moved from MCPC+ PluginClassLoader.
Combine reflection remapping into RemapperPreprocessor

Allows simultaneously extracting inheritance information,
and remapping reflection -- all in a single pass.