move shaders into .glsl files and add #include feature

src/node_panel_brush.h

@@ -111,7 +111,6 @@ class NodePanelBrushPreset : public Node
         float m_tip_angle = 0;
         float m_tip_angle_delay = 0;
         float m_tip_mix = 0;
-        float m_pattern_opacity = 0;
         float m_tip_wet = 0;
         float m_tip_noise = 0;
         float m_tip_hue = 0;
@@ -158,6 +157,7 @@ class NodePanelBrushPreset : public Node
         float m_pattern_brightness = 0.5f;
         float m_pattern_contrast = 0.5f;
         bool m_pattern_rand_offset = false;
+        float m_pattern_depth = 1.f;
     };
 public:
     std::function<void(Node* target, std::shared_ptr<Brush>& brush)> on_brush_changed;