Consider alternatives to get information from JavaScript tracker

[adatzer]

Is your feature request related to a problem? Please describe.
At the moment the way to get information (getDomainUserInfo, getUserId etc) from a JavaScript tracker is through callbacks. Tracker callbacks are called with the trackers dictionary as context. That way the callback can access the trackers dictionary using this.
However, this cannot be used when the JavaScript tracker is loaded in GTM:

• in tag template code this is a reserved keyword
• in custom HTML tags and in JS variables, this is not the trackers dictionary inside the callback

Describe the solution you'd like
A way to get information from a JavaScript tracker that is independent of this and possibly without providing access to trackers dictionary.
Even though this is currently a problem only when the JavaScript tracker is injected through this specific environment (GTM), providing an alternative way to get information from a JavaScript tracker may make sense in a wider scope.