Use safer type annotations

[Noam-Bendelac]

Primarily in playlists.ts, I'm using type annotations like

{
  action: 'comment',
  message,
  timestamp: new Date(),
  userId: res.locals.userId,
} as SituatedChatEvent

For auto-completion convenience, however this is very unsafe as a property could be missing and typescript would not give me an error (similar to the problems in microsoft/TypeScript#7481 (comment) and that issue in general). It seems the best way to fix this is either to move expressions like this into a temporary variable with a variable: Type annotation, or wrap the expressions in a util function like

function asType<T>(value: T) {
  return value;
};

As suggested in the linked issue.

[Noam-Bendelac]

This is affecting the removed tracks feature #87 as that involves changing API and DB types. These problematic type assertions are present both in the backend and in the frontend in places like SavedSongRow.tsx: { message } as PutTrackRemovedRequest