Backport of validation: don't strip marks from variables during validation into v1.13

[github-actions]

Backport

This PR is auto-generated from #37595 to be assessed for backporting due to the inclusion of the label 1.13-backport.

The below text is copied from the body of the original PR.

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There is custom logic for variable validations, explained in the surrounding comment. This was actually also stripping away sensitive and ephemeral metadata (or more accurately, just not adding it). This metadata is added by the usual approach of generating the HCL context. This meant errors during variable validation would expose sensitive values.

This PR updates the custom logic so that it only generates the value itself during the validate walk (which is the only time the custom logic is actually needed). For the validate walk, all variables are unknown anyway so the metadata doesn't matter.

Now, during other walks (eg. plan and apply) the real data is used, that does have the sensitive metadata attached. This means the sensitive metadata is no longer being exposed.

Target Release

1.13.2

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.

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Overview of commits

• 45fac94

• 27ea08b

[github-actions]

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