Refactor workspace constants, constant usage, and related code/docs

Issue: Refactorings to workspace container/script logic (#511503 - closed)

What does this MR do and why?

Refactors workspace constants, constant usage, and related code/docs:

• Extracts some "magic strings" repeated across multiple files to shared constants
• Removes unnecessary fully-qualified namespaces from some constant usages
• Refactors ROP chain to pass along tools_dir in context, and thus simplify some of the ROP chain steps to not be directly coupled to the volume/path in the context.
• Refactors declaration and usages of constants across the Workspaces domain code
• Documents standards for constant usage within Workspaces domain code
• Removes some unused Message module includes
• Some other minor header style formatting changes to the domain README file (headers shouldn't use Title Case)

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• Refactorings to workspace container/script logic (#511503 - closed)
• Startup scripts for Remote Development workspac... (&15602)

MR acceptance checklist

Please evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Screenshots or screen recordings

Pure refactoring, no UI changes.

How to set up and validate locally

All tests should pass, and all Workspaces functionality should have no regressions.