editor: Add generic navigation overlays

[GoldStrikeArch]

Overview

Adds a generic editor-owned navigation overlay primitive for rendering target ranges, anchored labels, and fade ranges. This gives Helix amp jump, Beam Jump, and future jump-style features (like this one) a shared editor abstraction for overlay layout and paint instead of feature-specific render paths.

Self-Review Checklist:

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Closes #52629

Release Notes:

• N/A