Ensure we cleanup the marshalling for elements of collections (stateful and stateless)

[jkoritzinsky]

We accidentally lost the element marshalling when moving to the released marshaller design. This PR adds it back with matching logic to the previous marshaller design.

Verified manually that we emit the right code for the case in #76584

Fixes #76584

Given the scope of the break that this fixes (memory leaks), I think this is a backport candidate.

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Issue Details

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We accidentally lost the element marshalling when moving to the released marshaller design. This PR adds it back with matching logic to the previous marshaller design.

Verified manually that we emit the right code for the case in #76584

Fixes #76584

Given the scope of the break that this fixes (memory leaks), I think this is a backport candidate.

Author:	jkoritzinsky
Assignees:	-
Labels:	area-System.Runtime.InteropServices, source-generator
Milestone:	-

[elinor-fung]

What do you think about adding tests that just validate the Free of a marshaller implementation gets called? Similar to ones we have for OnInvoked and the guaranteed unmarshalling methods.

[jkoritzinsky]

I'll try to come up with a test.

[AaronRobinsonMSFT]

Given the scope of the break that this fixes (memory leaks), I think this is a backport candidate.

Yes, it is.

[AaronRobinsonMSFT]

/backport to release/7.0

[github-actions]

Started backporting to release/7.0: https://github.com/dotnet/runtime/actions/runs/3193476808