Add error diagnostics when receiving an unknown value from ReadResource or UpgradeResourceState

[jbardin]

Add error diagnostics to catch when we find an unknown value from ReadResource or UpgradeResourceState. An unknown value is not valid in either of these cases, but the current error is not helpful and only returns a generic error about failed state serialization.

Fixes #34502
Fixes #34503

[bflad]

Straightforward enough! I'm personally okay with the generic/easier implementation of saying there's unknown values somewhere, rather than spending effort on a more in-depth walk to output the paths to those unknown values. I'm hoping we'll do that more exhaustive solution on the provider side to ease fixing this situation.

Do we want/need to do this with the very new MoveResourceState too while we're here?

Regardless, looks good to me.

[jbardin]

Yeah, this is something that shouldn’t have gotten this far in the first place, but we at least want a useful message. I don’t think we need to dig too deep, which would also mean formatting complex structures and dealing with sensitive values. I’ll add the same check to MoveResourceState while we’re at it!

[github-actions]

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[github-actions]

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