Export TID300 - Point class

[md-prog]

This is to prepare dcmjs library to separate Cornerstone Adapter as a separate package.

https://github.com/dcmjs-org/dcmjs/pull/320#issuecomment-1275178945

In Cornerstone3D adapter code, the utilities/TID300/Point is being used, but this one is not publicly exported from dcmjs.