Completed call_highs_from_csharp.cs by passing a Hessian and resolving #2974

Job	Run time
debug (ubuntu-latest)	3m 27s
debug_all_tests (ubuntu-latest)	3m 37s
debug64 (ubuntu-latest)	3m 41s
debug64_all_tests (ubuntu-latest)	3m 42s
release (ubuntu-latest)	3m 24s
release_all_tests (ubuntu-latest)	3m 32s
Release64 (ubuntu-latest)	3m 17s
Release64_all_tests (ubuntu-latest)	3m 33s
	28m 13s

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