chore(docs): Brillig VM docs

[vezenovm]

Description

Problem*

Resolves #8125

Summary*

Went through https://noir-lang.github.io/noir/docs/brillig_vm/ to see where we were missing documentation. This should cover missing documentation on any structs/enums/modules/etc.

Additional Context

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.