Add encodeValue and decodeValue using serializer<T>()

[findusl]

kotlinx.serialization provides a utility function to determine the serializer of a type. It makes using the encodeValue and decodeValue APIs even easier.

I will add more and cleaner tests (not just foo2), if you are interested in this change. I just thought I check before putting in the work. You might have some reason to avoid this function.

[russhwolf]

Thanks! I wasn't aware that the auto-detecting serializer machinery worked on non-JVM targets (hadn't really looked closely at that in a couple years), so that's the only reason this isn't already in there.

In addition to tests, I'd also like to add KSerializer-free versions of the rest of the APIs. I can help out there if you're uncertain about anything.

(Once that's done, it's past time to split SettingsSerialization.kt into multiple files, but I'll handle that later in a follow-up)

[findusl]

According to this page, it should be part of common. There is some special version for the JVM though, maybe that confused you: https://kotlinlang.org/api/kotlinx.serialization/kotlinx-serialization-core/kotlinx.serialization/serializer.html

I added all the functions and duplicated all the basic tests. I also added test cases for the Exception, when a class is not serializable.

And the file is definitely too big now. But I'll leave that up to you.

[russhwolf]

Thanks for this! I've rebased and merged it into a new branch which will make up the 1.2.0 release.