• fixes: Polygon 2D grid snap does not function consistently #110966

Issue Description

When we drag a vertex of a Polygon from polygon editor.

• Pressed mouse left key, record mouse position as drag_from
• Drag to somewhere and release mouse, get mouse position as drag_to, depending on grid snap configuration, we will calculate with snap_point() to let mouse position snap to the grid
• The problem is we used drag_to - drag_from as distance to update points of polygon, that caused very hard to drag a vertex to snap the grid correctly. It should use snapped mouse position directly.

e.g.

• vertex position (1, 1)
• grid (10, 10)
• original mouse position (5, 5), we pressed mouse on (5,5)
• target mouse position (10, 10), we released mouse on (10, 10). Maybe real position is (9,9) or (11,11), it will be snapped to (10, 10) as grid configuration.
• The the distance is (10, 10) - (5, 5) = (5,5)
• Finally, vertex will move to (1, 1) + (5,5) = (6,6), which is not snapped on grid.
• We should let vertext move to (10, 10) directly.