If a declaration is annotated both with SinceKotlin and WasExperimental
and the SinceKotlin version makes it inaccessible, the experimental
checker must regard it as experimental, with markers specified in the
WasExperimental annotation arguments. So only errors/warnings about the
experimentality are going to be reported in this case, and no error that
the declaration is unavailable because of a low API version
For example, if a class is `@SinceKotlin("X")
@WasExperimental(M::class)`, then its constructor should also be
accessible if API < X, provided that the opt-in to M is given
Usages of declarations annotated with WasExperimental are allowed even
if the API version requirement is not satisfied, provided that the
opt-in to all mentioned markers is given. This is needed for smooth
graduation of API in kotlin-stdlib
Alexander Udalov