Checks: Refactor existing check addrs and add new check block addr

[liamcervante]

This PR adds an address structure for referencing the new Check blocks within Terraform. As part of this, I have refactored the existing Check address structure and Checkable interface.

• Renamed the old Check address structure to CheckRule to better describe what it is actually referencing, and meaning we can use the name Check to reference actual Check blocks.
• Moved the new CheckRule address and Checkable interface into their own files.
• Introduced a new Check address that describes a single Check block.

For now, the actual Check blocks don't exist yet so nothing is referencing the new Check addresses yet.

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This PR is part of chain of PRs introducing the new Checks feature into Terraform for v1.5. The chain of PRs is as follows:

Branch	Description	Pull Request
liamcervante/checks/scoped	Add support for scoped resources.	#32732
liamcervante/checks/addr	Add Terraform addresses for new Check blocks.	#32733
liamcervante/checks/configs	Add config parsing new Check blocks.	#32734
liamcervante/checks/graph	Add nodes and transforms for processing new Check blocks.	#32735

I have created the chain to make reviewing the smaller contained part of the process easier. IF you want to view all the changes together in a single PR, navigate to the last PR in the chain and compare it to the main branch and you will see all changes from all prior PRs in a single place.

[alisdair]

Looks good to me! I was concerned that this change modified the enum types, and didn't update the state file decoding/encoding. But I see that's handled as part of #32735 so that's fine.

[github-actions]

Reminder for the merging maintainer: if this is a user-visible change, please update the changelog on the appropriate release branch.

[github-actions]

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