Plugins: Allow apps to expose components. Update the extensions API. (#87236)

* feat: introduce exposable components and update the public APIs

Co-authored-by: Marcus Andersson <marcus.andersson@grafana.com>

* tests: fix the tests for `usePluginComponent()`

I broke them when I wrapped the component with the PluginContextProvider which fetches the plugin metadata.

* fix: typo

---------

Co-authored-by: Marcus Andersson <marcus.andersson@grafana.com>

packages/grafana-runtime/src/services/pluginExtensions/getPluginExtensions.ts

@@ -25,6 +25,11 @@ export type UsePluginExtensionsResult<T = PluginExtension> = {
   isLoading: boolean;
 };
 
+export type UsePluginComponentResult<Props = {}> = {
+  component: React.ComponentType<Props> | undefined | null;
+  isLoading: boolean;
+};
+
 let singleton: GetPluginExtensions | undefined;
 
 export function setPluginExtensionGetter(instance: GetPluginExtensions): void {