feat: Add simplified S-Pen implementation

- Clean S-Pen implementation with hover guard and proximity detection
- Virtual barrel pointer system for libretro compatibility
- Stylus tool type detection (AMOTION_EVENT_TOOL_TYPE_STYLUS)
- Side button (barrel) functionality for hover-drag
- Contact-based clicking behavior
- Native touchscreen consistency (no coordinate updates during hover)
- Proper Android platform guards

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Co-Authored-By: Claude <noreply@anthropic.com>

Author: f4mrfaux