This fixes an issue I originally introduced in #2216. The original PR and this PR try to modify the graph transformation process as little as possible due to it's complexity.

Unfortunately, I introduced a path in #2216 for apply that does not apply to destroy operations. In both apply and destroy, we aggressively prune the graph to minimize what actually needs to be evaluated in order to make the necessary changes. This work is done in the pruneUnusedNodesTransformer and relies upon some very specific interface implementation and dense logic.

For #2216, I needed to ensure that variable blocks that have validations are not pruned out from the graph between plan -> apply. I introduced an interface implementation that allows the node to say "Hey! I still need to exist! Don't prune me!". That worked reasonably well for the standard apply scenario, and I added a test to confirm.

However, I did not fully understand the implications for destroy. During a destroy action, the variables should be pruned from the graph and the check not run, as the data it's targeting won't exist (the reason for the check/validation). When it is not pruned, it keeps "configuration" nodes within the apply graph which do not function correctly during destroy operations.

This is not an ideal solution, but it has a very small likelihood of breaking existing workflows. As evidenced by the complexity described above, this is a very tricky thing to modify correctly, and the smaller the change we can make, the better. Longer term, I hope that something that comes out of #3078 will allow us to simplify this whole process.

I still need to add a bespoke test case to context_apply2_test.go and update the changelog

Resolves #3126

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