Support for kotlinx.io

[DRSchlaubi]

Since we alreafy have support for okio (See #1901) it would make sense to also support the new kotlinx.io library for the same purposes.

The remaining question is, where to put it, either create a new module like for okio or add it to the json module itself since it is a official library

[sandwwraith]

There's also #253 :) kotlinx-io is being developed from scratch now, so APIs are rapidly changing. I think after several releases, we can start incorporating it.