[Testing Framework] Add test command to Terraform CLI

[liamcervante]

This PR adds the test command back into Terraform, and connects all the previous PRs into a functional testing framework.

Target Release

1.6.0

Terraform Testing Framework

This PR is part of a chain of PRs implementing the new Terraform test command.

Description	Branch	PR
Cleanup previous implementation	liamcervante/tests/cleanup	#33323
Add initial human view implementation	liamcervante/tests/view	#33324
Add Terraform test file config support	liamcervante/tests/config	#33325
Update terraform context functionality	liamcervante/tests/context	#33326
Add test command to Terraform CLI	liamcervante/tests/command	#33327

The above PRs implement the core functionality of the new test command. More PRs will follow implementing specific features, but the test command will work end-to-end once the above PRs are merged.

These changes are implemented in a chain, with each change building on the previous one to ensure ease of review. To see the combined changes as one, navigate to the last PR in the chain and change it to merge directly into main.

[jbardin]

I think this looks good to get the command into a usable state for additional testing. If test is not going to make use of the local backend for running plans and applies, we are going to need to make sure some of that framework gets replicated within the test command. Plugin validation and process cancelation are the first to things that come to mind.

[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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