Conform more of the codebase with noImplicitAny and strictNullChecks (#25174

* Conform more of the codebase with `noImplicitAny` and `strictNullChecks`

* Fix tests

* Update src/vector/app.tsx

src/vector/platform/VectorBasePlatform.ts

@@ -30,7 +30,7 @@ import Favicon from "../../favicon";
 export default abstract class VectorBasePlatform extends BasePlatform {
     protected _favicon: Favicon;
 
-    public async getConfig(): Promise<IConfigOptions> {
+    public async getConfig(): Promise<IConfigOptions | undefined> {
         return getVectorConfig();
     }