A driver reading `Object.hide_viewport` would break when that object was
hidden. Hidden objects don't have the `OBJECT_BASE_FLAGS` node in the
depsgraph, but that node was required for the driver to work.
Now the `OBJECT_FROM_LAYER` component (which optionally contains the
`OBJECT_FROM_LAYER` node) has explicit `ENTRY` and `EXIT` nodes, which
are used for relations with other components. These relations now remain
valid, even when the `OBJECT_FROM_LAYER` node is absent.
Differential Revision: https://developer.blender.org/D8124
Reviewed By: sergey
c7694185c9