Move towards user-friendly ways of triggering baking lightmaps (and eventually reflection probes)

Building on the cleaned up DebugView (QTBUG-109814)
Move away from the "launch with command-line argument to trigger baking and then exit" and add an interactive way to trigger baking from the DebugView. This then naturally applies to Design Studio as well (which could have a "Bake" button, invoking the same internal APIs, though we won't implement that here, just provide the enablers)

See image below:

(design can change (could be another tab, the tab could be renamed, etc.) but the concept applies)