Only display the overlays for nodes that are in the viewer render path and have their properties panel maximized.

[devernay]

Currently:

• overlays for all open properties panels are displayed, even those that are not in the render path for the current viewer (e.g. a Transform node connected to nothing

• overlays for minimized properties panels are not properly updated (updating requires moving the mouse over the viewer).

We propose to only draw overlays that are in the render path for the current viewer, and for which the properties panels are open and maximized. If the viewer has several inputs connected, overlays for all inputs will be displayed.

This will be switchable by a preference setting (last item in Preferences/Viewer)

See also #691 (comment)