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)

api/src/utils/deep-map.ts

@@ -1,6 +1,7 @@
 export function deepMap(
 	object: Record<string, any>,
 	iterator: (value: any, key: string | number) => any,
+	// eslint-disable-next-line @typescript-eslint/explicit-module-boundary-types
 	context?: any
 ): any {
 	if (Array.isArray(object)) {