Add test to ensure Results object is populated fully

[mrmundt]

Fixes None (but is part of #3688)

Summary/Motivation:

We want to ensure that all of the new solvers are populating the new and improved Results object fully with all the extra lovely info. This test ensures that this is completed.

Changes proposed in this PR:

• Add test_results_object_populated that enforces that the Results object is fully populated for each solver
• Fix HiGHS to populate missing pieces

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[michaelbynum]

Nice!