[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.
[MWF] Fix opacity of form (#19856)

Change-Id: I2d3d31516f8105b059fa63838f81e4b066179f60