Syntax fixes (#5367)

* Declare return types on functions

And a very few other type related minor fixes

* Minor syntax fixes

* Remove unnecessary escape chars in regexes
* Remove unnecessary awaits
* Replace deprecated req.connection with req.socket
* Replace deprecated upload with uploadOne
* Remove unnecessary eslint-disable-next-line comments
* Comment empty functions / catch or finally clauses
* Fix irregular whitespaces
* Add missing returns (null)
* Remove unreachable code
* A few logical fixes
* Remove / Handle non-null assertions which are certainly unnecessary (e.g. in
tests)

app/src/composables/unsaved-changes/unsaved-changes.ts

@@ -1,6 +1,6 @@
 import { onBeforeMount, onBeforeUnmount, Ref } from '@vue/composition-api';
 
-export default function unsavedChanges(isSavable: Ref<boolean>) {
+export default function unsavedChanges(isSavable: Ref<boolean>): void {
 	onBeforeMount(() => {
 		window.addEventListener('beforeunload', beforeUnload);
 	});