frontend-plugin-api: swtich IconApi.listIconKeys to return an array direcly instead

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/frontend-plugin-api/api-report.md

@@ -981,9 +981,7 @@ export interface IconsApi {
   // (undocumented)
   getIcon(key: string): IconComponent | undefined;
   // (undocumented)
-  listIconKeys(): {
-    keys: Iterable<string>;
-  };
+  listIconKeys(): string[];
 }
 
 // @public

packages/frontend-plugin-api/src/apis/definitions/IconsApi.ts

@@ -25,7 +25,7 @@ import { IconComponent } from '../../icons';
 export interface IconsApi {
   getIcon(key: string): IconComponent | undefined;
 
-  listIconKeys(): { keys: Iterable<string> };
+  listIconKeys(): string[];
 }
 
 /**