MultipartHelper, MultipartHelper$ and MultipartHelper$IPartTileConverter are
all public-member- and descriptor-identical to the reference, and the full
emitted class list is unchanged -- this port neither adds nor removes a class.
MultipartHelper gains a private constructor and its companion's class
initializer loses ACC_PUBLIC, neither of which is nameable by a caller.
MultipartHelper$ was kept deliberately. It is not among the 17 MODULE$
singletons read from bytecode and no jar links against it, but guidenh names it
as a reflective string, and removing a companion breaks that invisibly.
createTileFromParts now builds one JavaConversions wrapper for both calls
instead of one per call site, and convertMulti returns Collections.emptyList or
singletonList instead of a Scala Seq wrapper. The declared type was always
java.lang.Iterable.
107 plain-JVM tests and 10 Forge server tests pass unchanged.
