Add Wrappers#IteratorWrapper MiMa filter

[regadas]

Follow up to issue # scala/bug#12344 and PR #9507

[dwijnand]

What requires this? If I run mima on the current HEAD of 2.12.x it doesn't seem to be required:

> library/mimaReportBinaryIssues
[success] Total time: 3 s, completed 18-Feb-2021 08:02:31
> show library/mima
mimaBackwardIssueFilters   mimaBinaryIssueFilters     mimaCheckDirection         mimaCurrentClassfiles      mimaDependencyResolution   mimaFailOnNoPrevious       mimaFiltersDirectory
mimaFindBinaryIssues       mimaForwardIssueFilters    mimaPreviousArtifacts      mimaPreviousClassfiles     mimaReportBinaryIssues
> show library/mimaBinaryIssueFilters
[info] * ExcludeByName[Problem]("scala.reflect.internal.*")
[info] * ExcludeByName[MissingClassProblem]("scala.collection.immutable.TreeSet$unitsIterator$")
[info] * ExcludeByName[Problem]("scala.collection.immutable.NewRedBlackTree*")
[success] Total time: 0 s, completed 18-Feb-2021 08:02:44