Revisit whether layer with hidden image should be considered in top-logic

[Jdaviz-Triage-Bot]

Reporter: Kyle Conroy

A layer can be visible, but the image hidden (and contours either enabled or not).  Currently as long as the layer itself is visible, that layer is considered when determining the top label (for coordinates display, compass, etc) in all image viewers (cubeviz and imviz).  We may want to revisit this behavior as it may be unexpected, especially when both the image and contours are disabled.

See #1445

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