title: How to get all minted tokenIDs?
body: <p>I'm wondering how to retrieve all minted tokenIDs by a certain ERC721 contract?
  What I'm trying to do is retrieve an array with all minted tokenIDs.</p>
  <p>For example:
  I want to have a function that returns an array of tokenIds that exist.
  Let's say 1 and 48 (max supply) are minted the function needs to return: [1,48]. This means I still have 2-47 left to be minted</p>
  <p>I couldn't find anything about this only solutions where you would have to enter an address or an index.</p>