Show clear plugin startup errors in Studio

When a plugin prevents an application from starting, Studio can leave the developer with only "Exit code 1", without explaining which plugin failed or how to resolve the problem. This can happen even in an empty application that never calls a plugin method.

Show the underlying plugin diagnostic in Studio's run/debug error presentation, including the affected package, a clear explanation of the failure, and an appropriate next step. For a dependency whose types cannot be shared between plugins, explain that the plugin author must package the supplying assembly as shared.