Fix MAGN-5489

<h4>Summary</h4>

It is not safe for concurrent threads to modify/delete geometry entities in the geometry library at the same time. Most time, the entities will be disposed by the evaluation thread. But sometimes, if there are intermediate geometry entities, they will be disposed by a different thread. As a result, a lot of weird issues are caused.

This submission fixes the defect by disposing intermediate geometry entities explicitly.

<h4>Reviewers</h4>
@lukechurch 
@hlp 
@pboyer 

PTAL
using(var converted = ....) would have helped.