This implementation only checks annotations set on expect/actual
declarations and requires further refinement (e.g. checking of other
annotation targets, class scopes within typealiases).
^KT-58551
This commits adds a new annotation OptionalExpectation to the standard
library, which is experimental. To enable its usage, either pass
'-Xuse-experimental=kotlin.ExperimentalMultiplatform' as a compiler
argument, or '-Xuse-experimental=kotlin.Experimental' and also annotate
each usage with `@UseExperimental(ExperimentalMultiplatform::class)`
#KT-18882 Fixed
Roman Efremov