Enhance KotlinSerializer with value codecs for widening primitive conversion.

[vbabanin]

JAVA-5303

[rozza]

Kotlinx Json has a configuration to allow for lenient parsing: https://github.com/Kotlin/kotlinx.serialization/blob/master/docs/json.md#lenient-parsing

Should this be configurable?

[jyemin]

@rozza I think in this case it's better to be consistent with other codecs and also with the way numeric values are treated in MongoDB is basically interchangeable and compatible with each other, so long as there is no loss of precision or magnitude.

[jyemin]

@vbabanin can this come out of Draft now?