Add DAG data parsing utils

What does this MR do?

The next wave in #215517 (closed), this MR adds the utilities needed to parse the data we receive from the endpoints in order to prepare it for the graph layout. Don't worry — there are lots of comments in the file explaining what the transformation looks like.

This is reliant on !32460 (merged) merging which is still blocked by the backend MR.

Note: This is a continuation of !32692 (closed), because my shenanigans did not fool our MR methods.

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Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.