Rename ClassFile::transform to ClassFile::transformClass

ClassFile::transform was initially ClassModel::transform, which transforms the receiver class model to a new class byte array. This functionality was in parallel with ClassBuilder::transform, which accepts a ClassModel and a ClassTransform and forwards the results to the receiver builder.

After the ClassFile context object introduction, ClassModel::transform becomes ClassFile::transform; now, its role is more similar to ClassBuilder::transformMethod, ClassBuilder::transformField, or MethodBuilder::transformCode (transforming subtypes), and it's confusing with ClassFileBuilder::transform (which accepts the same model type as the built type). We should rename ClassFile::transform to ClassFile::transformClass to make this method's role more clear.