Add support for eqR_a ABC instruction

What does this MR do?

Adds support for the eqR_a ABC instruction.

Changes to public APIs

N/A

Author's checklist (required)

• If bugs have been solved, tests have been added (guidelines)
• A changelog entry has been added (guidelines)
• Newly added code is documented (guidelines)
• Newly added code has a style consistent with the rest of the repository
• Intermediate commits compile (use git rebase -i main if not)

Related issues

Closes #131 (closed)