Don’t throw (harmless) error if no CODAP callback
delay dgExporter init until interactive load

[#79814268]

Previously, redirected interactives to fail to connect to CODAP because dgExporter was inited in the initial load of the interactive (which doesn’t initialize an interactive but just reloads the page), swallowing the codap-present message. Now we only init when the interactive
no point in dispatching event from constructor…

[#79814268]