BUG: Fix "orphan view" issue in layout manager

The widget visibility is now set considering both the MappedInLayout
and the Visibility view node properties.

It fixes a regression re-introduced in r24209 (ENH: Update layout
view factory to consider view node visibility property) that was
originally fixed in r24175 (BUG: Fixed orphaned views displayed in
secondary layout widgets).

This commit also extends vtkMRMLAbstractViewNode API adding:

• IsMappedInLayout() / SetMappedInLayout()
• IsViewVisibleInLayout()

Test "qMRMLLayoutManagerVisibilityTest" has also been updated to check
the value returned by "IsMappedInLayout()", "IsViewVisibleInLayout()"
and "GetVisibility()".

Note also that functions "IsMappedInLayout()" and "SetMappedInLayout()"
still set/get the "MappedInLayout" attribute. This was done to ensure
existing code relying on its value would still work.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24215 3bd1e089-480b-0410-8dfb-8563597acbee