Improve failure message on encountering unknown key in JSON

[qwwdfsad]

Right now, the failure is the following:

Exception in thread "main" kotlinx.serialization.json.internal.JsonDecodingException: Unexpected JSON token at offset 20: Encountered an unknown key 'version' at path: $.name
Use 'ignoreUnknownKeys = true' in 'Json {}' builder to ignore unknown keys.
JSON input: {"name":"unknown", "version": 2.0}
	at kotlinx.serialization.json.internal.JsonExceptionsKt.JsonDecodingException(JsonExceptions.kt:24)

Maybe it is worth making it more explicit and straightforward, for example:

Exception in thread "main" kotlinx.serialization.json.internal.JsonUnknownKeyException: Encountered an unknown key 'version' at path: $.name
Use 'ignoreUnknownKeys = true' in 'Json {}' builder to ignore unknown keys.
JSON input: {"name":"unknown", "version": 2.0}
	at kotlinx.serialization.json.internal.JsonExceptionsKt.JsonDecodingException(JsonExceptions.kt:24)

Note that the actual exception can still be internal

[sandwwraith]

The version you suggest lacks an offset, which may be important for large json inputs which do not fit in the hint

[qwwdfsad]

Well, it can be put after the main message. The problem with the current one is that it first explains where things went wrong instead of what went wrong