Update RESTRUCTURE.md to include latest changes

[bvandermoon]

Description

Update RESTRUCTURING.md to include the latest changes. We made some changes to this structure to better support upcoming versioning work.

The most notable changes are to add an src parent directory and move tests to a higher level directory.

Tests

N/A - no code changes, only documentation

Checklist

Before submitting this PR, please make sure (put X in square brackets):

• I have performed a self-review of my code.
• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed.