Adjust Gradient layout using GuiStyle

[ueshita]

• Modified to use relative values of GuiStyle settings where direct values are specified.
• Modified to draw markers with Path (Make AA works)

The bellow is Windows display scaling 125%

before

after

[Copilot]

Pull Request Overview

This PR adjusts the gradient layout by applying GuiStyle settings for relative sizing and improves marker rendering by drawing them with a new path approach that handles different marker directions.

• Use relative values from GuiStyle for margins and sizing.
• Introduce the MarkerDirection enum and update DrawMarker to render markers based on direction.
• Adjust grid and marker drawing dimensions to respond to current style settings.