Use anyOf for TS Unions

[WoH]

All Submissions:

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• Have you written unit tests?
• Have you written unit tests that cover the negative cases (i.e.: if bad data is submitted, does the library respond properly)?
• This PR is associated with an existing issue?

Closing issues

Closes #671

If this is a new feature submission:

• Has the issue had a maintainer respond to the issue and clarify that the feature is something that aligns with the goals and philosophy of the project?

Potential Problems With The Approach
If anyone was relying on this, admittedly suboptimal behavior, their code may break.

Buy Why
Our validation already does what anyOf should do. Also, it's a better reflection of TS Union checking as of right now.