Profiler should support importing profiles without React being connected

A user has reported frustrations with being unable to import a profile/trace into React DevTools when no app was connected. (This applies to both the browser extension (React DOM) and standalone DevTools (React Native). While the UX for this ask is clear enough, we should consider the following: * Browser extension: Is it confusing to change React DevTools to show for non-React websites? * Standalone: Where will we show the connection instructions if we show the DevTools UI? (The splash UI is usually a page of instructions on how to connect.) * Does anything else break when the UI is shown without at least one connected renderer?