core-api: default type parameters for BackstagePlugin to avoid breakage

Co-authored-by: blam <ben@blam.sh>

packages/core-api/src/plugin/Plugin.tsx

@@ -93,8 +93,8 @@ export class PluginImpl<
 }
 
 export function createPlugin<
-  Routes extends AnyRoutes,
-  ExternalRoutes extends AnyExternalRoutes
+  Routes extends AnyRoutes = {},
+  ExternalRoutes extends AnyExternalRoutes = {}
 >(
   config: PluginConfig<Routes, ExternalRoutes>,
 ): BackstagePlugin<Routes, ExternalRoutes> {

packages/core-api/src/plugin/types.ts

@@ -76,8 +76,8 @@ export type AnyRoutes = { [name: string]: RouteRef<any> };
 export type AnyExternalRoutes = { [name: string]: ExternalRouteRef };
 
 export type BackstagePlugin<
-  Routes extends AnyRoutes,
-  ExternalRoutes extends AnyExternalRoutes
+  Routes extends AnyRoutes = {},
+  ExternalRoutes extends AnyExternalRoutes = {}
 > = {
   getId(): string;
   output(): PluginOutput[];