vim: Remap cursor position with display_point

[HuaGu-Dragon]

Objective

• Fixes Helix mode multi-cursors broken by inlay hints #53650
• Possibly also fixes helix: duplicate cursor below seems broken on go files #57956 (needs confirmation)

Solution

• Replace the direct DisplayPoint::new(row, col) construction with a proper buffer-point-to-display-point
• This goes through the full inlay → fold → tab → wrap → block pipeline and correctly accounts for any inlay hints on the target line.

Testing

• Added a regression test for multi-cursors with inlay hints in helix mode

Self-Review Checklist:

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

Release Notes:

• Fixed Shift+C cursor position with inlay hints in helix mode