feat(ssa): Post dominator tree

[vezenovm]

Description

Problem*

Resolves #7571

Summary*

This PR is mostly contained to tests as it will be the basis for further control dependence analysis.

1. Logic for reversing the CFG
2. Switched post order computation to use the CFG rather than the function definition
3. Add a test to show using the the reversed CFG and updated post order provides an accurate post-dominator tree

Additional Context

The new reverse and with_function_post_dom methods are only used in tests. The #[cfg(test)] attribute will be removed as these methods are used by later work.

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.