Add integration with kotlinx-io library

[sandwwraith]

Integration is similar to Okio's one with functions encodeToSink, decodeFromSource, etc.

Fixes #253

[sandwwraith]

The main question is how to name module/package:

kotlinx.serialization.json.kxio (as now) — a cryptic abbreviation
kotlinx.serialization.json.kotlinx.io — duplication of 'kotlinx'
kotlinx.serialization.json.io — not clear which IO we are referring to (we also have kotlinx.serialization.json.okio currently)

[fzhinkin]

The main question is how to name module/package:

kotlinx.serialization.json.kxio (as now) — a cryptic abbreviation

Personally, I like this one (most likely because I used to shorten the library name to kx-io), but indeed it looks a bit cryptic.

[fzhinkin]

For some reason, this particular benchmark shows worse results compared to Okio version. It doesn't block integration in any way, I'll check the root cause later.

[fzhinkin]

That's a perf issue on the kotlinx-io size: an extension function to read code point values is defined only on Source and it performs a few actions to fill the inner buffer before decoding the code point. In Okio, that's a member function with a different (and optimized) implementation for Buffer.
kx-io should do the same: Kotlin/kotlinx-io#342.

[Dominaezzz]

kotlinx.serialization.json.io — not clear which IO we are referring to

I think this is best. This library is under kotlinx so it's sensible for the default io to also be the kotlinx one.

Any duplicate mention of kotlinx, be it the abbreviation kx or the full thing kotlinx just seems like a waste of characters imo.

[DRSchlaubi]

I think this is best. This library is under kotlinx so it's sensible for the default io to also be the kotlinx one.

Have to agree with that one, but what about simply including it like kx-datetime supports kx.ser out of the box, or does this run into the issue of compileOnly not working on non-jvm platforms?

[sandwwraith]

@DRSchlaubi Yes, kotlinx-datetime actually uses api dependency for Js and Native.

[sandwwraith]

Let's stick with kotlinx.serialization.json.io then.