fix: Line tool diagonal snapping and angle

[StickmanRed]

Description

Fixes two issues in the Line tool: line snapping not working when drawing a diagonal line, and angle to draw diagonal lines being slightly off.

Testing

1. Open the Line tool and draw a line on the canvas.
2. Hold Shift to draw another line diagonally, and snap to a vertex on the first line. When snapping, the line's endpoint should not move with the mouse.
3. Move the endpoint to a 22.5 degree angle, halfway between diagonal and horizontal/vertical. The line should switch between diagonal and horizontal/vertical around this halfway angle.

Line.tool.mp4