Add auto-scroll during drag selection

[ChristmasSun]

Pull Request

When selecting text by click dragging, the editor does not auto-scroll when the cursor reaches the edge of the viewport. This affects both horizontal (long lines) and vertical (many lines) selection. This pull request adds in this auto-scroll functionality.

Description

• Add useDragScroll hook that auto-scrolls the textarea during drag selection when the cursor is near or beyond viewport edges
• Scroll speed scales proportionally to cursor distance from the edge
• Uses a single requestAnimationFrame loop, refs only (no state, no re-renders), zero work when not dragging
• Dispatches scroll events to keep overlay layers in sync
• Skip ensureCursorVisible during active drag-scroll to prevent viewport fighting

Suggested Labels

Editor

Screenshots/Videos

changes.mp4

Checklist

• [ x ] I have read and will follow the Code of Conduct.
• [ x ] I have read and agree to the
  Contributor License and Feedback Agreement.

[mehmetozguldev]

Legit perfect, thank you!