Scale Tree.INCREMENT by zoom level instead of using fixed pixels

[ShahzaibIbrahim]

The Tree.INCREMENT constant defines how many pixels the horizontal scrollbar jumps when clicking the left or right buttons. Previously, this was a fixed pixel value, which made scrolling feel too small on high-DPI monitors.

This change redefines INCREMENT in points and converts it to pixels based on the current zoom level, ensuring consistent scrolling increments across different display scales.