failing resource instance apply should keep prior state

[DanielMSchmidt]

This is a code path that can not be taken in normal Terraform, but when TF is used through the RPC API we can end up in these situation, so we should make sure Terraform does not remove the state when an apply fails.

Fixes #

Target Release

1.15.x

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.

[nfagerlund]

I manually tested this with my live repro of the bug, using a Terraform build with this patch applied but without the locals fix from #37980. We're good!

• As expected, the plan showed "known after apply" for attrs but didn't error, and allowed me to proceed to apply. (#37980 fixes that.)
• As expected, the apply errored and failed with aws_amplify_app.default still contains unknown values during apply (this is a bug in Terraform; please report it!).
• As hoped for, a subsequent plan and apply with the configuration repaired produced no changes! The errored resource was not removed from state.

[github-actions]

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