Enable @typescript-eslint/explicit-function-return-type in /src (#9788)

* Enable `@typescript-eslint/explicit-member-accessibility` on /src

* Prettier

* Enable `@typescript-eslint/explicit-function-return-type` in /src

* Fix types

* tsc strict fixes

* Delint

* Fix test

* Fix bad merge

src/Terms.ts

@@ -75,7 +75,7 @@ export type TermsInteractionCallback = (
 export async function startTermsFlow(
     services: Service[],
     interactionCallback: TermsInteractionCallback = dialogTermsInteractionCallback,
-) {
+): Promise<void> {
     const termsPromises = services.map((s) => MatrixClientPeg.get().getTerms(s.serviceType, s.baseUrl));
 
     /*
@@ -176,7 +176,7 @@ export async function startTermsFlow(
             urlsForService,
         );
     });
-    return Promise.all(agreePromises);
+    await Promise.all(agreePromises);
 }
 
 export async function dialogTermsInteractionCallback(