[MWF] Add unit test for #19818
[MWF] Don't try to remove non-child control (#19818)

When removing a control from a controls collection we have to
check that the control is part of the collection. Otherwise
we shouldn't do anything.
Merge pull request #1038 from ermshiperete/bug-xamarin-19818

[MWF] Don't try to remove non-child control (#19818)