twttr is not defined js error

Problem

I noticed this issue when using an entity browser to display media bundles. One of them is a twitter media entity. The twitter widget gets loaded as it should, but we get a few errors in the console saying twttr is not defined.

Proposed solution

The issue is in the twitter.js file, where we check if twttr is not defined and load it from the //platform.twitter.com/widgets.js instead, but we have no guarantee that this file gets loaded before the init function gets called. Therefore, we need to call the init function in a callback (e.g. on script load: https://javascript.info/onload-onerror).