Add specific experimental annotation for Features which are planned by kotlinx.coroutines

[jcornaz]

Many features provided by miop, are actually planned to be implemented by kotlinx.coroutines which means that we hope to deprecate them here in favor of the kotlinx.coroutines' version as soon as it is published.

So the user should be warned when using features which are known to be replaced by a kotlinx.coroutines feature.

The annotation should also provide a reference to the kotlinx.coroutines issue.