Add comparator for *.kotlin_[metadata|module|builtins] files

*.kotlin_metadata files are generated by Kotlin compiler, I didn't found any tool to read/parse them (only some libraries which might support this format), but there a issue in kotlin bug tracker:

"Support a tool to print metadata of binary files produced by the Kotlin compiler" https://youtrack.jetbrains.com/issue/KT-26826

You encouraged to upvote it, and comment why its important for diffoscope & rb effort.

attached 2 different RingBuffer.kotlin_metadata files found in kotlin/collections/RingBuffer.kotlin_metadata from same android app (different versions) 1RingBuffer.kotlin_metadata2RingBuffer.kotlin_metadata

running file on above files will return "data" so support for 'file' command is currently missing.