[DRAFT] Transcribe proposed new state handling from Terraform Core

[SBGoods]

Description

Proposed new state data is constructed in the Terraform internal/plans/objchange package. This PR aims to transcribe the Terraform Core handling and accompanying tests into the framework, converting the cty types into terraform-plugin-go tftypes.

TODO

The algorithm transcription and initial testing are in a finished state, but before this PR can be merged to main, we need to preform regression testing against one of the major providers to ensure that our proposed new state handling doesn't differ from Terraform Core's across multiple versions of Terraform.

There are also some failing tests in server_planresourcechange_test.go that hardcode assumptions about the proposed new state coming from Terraform Core that will need to be fixed as well.

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.
N/A