Change signature of Plugin.stop to maybe async (#170225)

## Summary

Fix https://github.com/elastic/kibana/issues/83612

This PR doesn't change any behavior, as we're already supporting (and
awaiting) promises returned from `stop` calls to plugin, it just changes
the type's signature to reflect that.

Also removed empty `stop` methods from existing plugins to make
typescript happy.

---------

Co-authored-by: kibanamachine <42973632+kibanamachine@users.noreply.github.com>

examples/feature_control_examples/server/plugin.ts

@@ -83,8 +83,4 @@ export class FeatureControlsPluginExample
   start() {
     return {};
   }
-
-  stop() {
-    return {};
-  }
 }

examples/user_profile_examples/server/plugin.ts

@@ -76,8 +76,4 @@ export class UserProfilesPlugin implements Plugin<void, void, SetupDeps, StartDe
   start() {
     return {};
   }
-
-  stop() {
-    return {};
-  }
 }

packages/core/plugins/core-plugins-browser/src/plugin.ts

@@ -6,6 +6,7 @@
  * Side Public License, v 1.
  */
 
+import type { MaybePromise } from '@kbn/utility-types';
 import type { CoreStart, CoreSetup } from '@kbn/core-lifecycle-browser';
 
 /**
@@ -23,5 +24,5 @@ export interface Plugin<
 
   start(core: CoreStart, plugins: TPluginsStart): TStart;
 
-  stop?(): void;
+  stop?(): MaybePromise<void>;
 }

packages/core/plugins/core-plugins-browser/tsconfig.json

@@ -16,6 +16,7 @@
     "@kbn/core-base-common",
     "@kbn/core-lifecycle-browser",
     "@kbn/logging",
+    "@kbn/utility-types",
   ],
   "exclude": [
     "target/**/*",

packages/core/plugins/core-plugins-server/src/types.ts

@@ -8,7 +8,7 @@
 
 import { Observable } from 'rxjs';
 import { Type } from '@kbn/config-schema';
-import type { RecursiveReadonly } from '@kbn/utility-types';
+import type { RecursiveReadonly, MaybePromise } from '@kbn/utility-types';
 import type { PathConfigType } from '@kbn/utils';
 import type { LoggerFactory } from '@kbn/logging';
 import type {
@@ -297,7 +297,7 @@ export interface Plugin<
 
   start(core: CoreStart, plugins: TPluginsStart): TStart;
 
-  stop?(): void;
+  stop?(): MaybePromise<void>;
 }
 
 /**
@@ -317,7 +317,7 @@ export interface AsyncPlugin<
 
   start(core: CoreStart, plugins: TPluginsStart): TStart | Promise<TStart>;
 
-  stop?(): void;
+  stop?(): MaybePromise<void>;
 }
 
 /**

src/plugins/data_view_editor/public/plugin.tsx

@@ -73,8 +73,4 @@ export class DataViewEditorPlugin
       },
     };
   }
-
-  public stop() {
-    return {};
-  }
 }

src/plugins/data_view_field_editor/public/plugin.ts

@@ -55,8 +55,4 @@ export class IndexPatternFieldEditorPlugin
       DeleteRuntimeFieldProvider: getDeleteFieldProvider(openDeleteModal),
     };
   }
-
-  public stop() {
-    return {};
-  }
 }

x-pack/plugins/runtime_fields/public/plugin.ts

@@ -22,8 +22,4 @@ export class RuntimeFieldsPlugin
   public start(core: CoreStart, plugins: StartPlugins) {
     return {};
   }
-
-  public stop() {
-    return {};
-  }
 }

x-pack/plugins/security_solution/public/plugin.tsx

@@ -348,7 +348,7 @@ export class Plugin implements IPlugin<PluginSetup, PluginStart, SetupPlugins, S
   public stop() {
     this.queryService.stop();
     licenseService.stop();
-    return this.contract.getStopContract();
+    this.contract.getStopContract();
   }
 
   private lazyHelpersForRoutes() {