macos: reorganize, rename, put files in groups

macos/Sources/Helpers/SplitView/SplitView.Divider.swift

@@ -0,0 +1,68 @@
+import SwiftUI
+
+extension SplitView {
+    /// The split divider that is rendered and can be used to resize a split view.
+    struct Divider: View {
+        let direction: SplitViewDirection
+        let visibleSize: CGFloat
+        let invisibleSize: CGFloat
+        
+        private var visibleWidth: CGFloat? {
+            switch (direction) {
+            case .horizontal:
+                return visibleSize
+            case .vertical:
+                return nil
+            }
+        }
+        
+        private var visibleHeight: CGFloat? {
+            switch (direction) {
+            case .horizontal:
+                return nil
+            case .vertical:
+                return visibleSize
+            }
+        }
+        
+        private var invisibleWidth: CGFloat? {
+            switch (direction) {
+            case .horizontal:
+                return visibleSize + invisibleSize
+            case .vertical:
+                return nil
+            }
+        }
+        
+        private var invisibleHeight: CGFloat? {
+            switch (direction) {
+            case .horizontal:
+                return nil
+            case .vertical:
+                return visibleSize + invisibleSize
+            }
+        }
+        
+        var body: some View {
+            ZStack {
+                Color.clear
+                    .frame(width: invisibleWidth, height: invisibleHeight)
+                Rectangle()
+                    .fill(Color.gray)
+                    .frame(width: visibleWidth, height: visibleHeight)
+            }
+            .onHover { isHovered in
+                if (isHovered) {
+                    switch (direction) {
+                    case .horizontal:
+                        NSCursor.resizeLeftRight.push()
+                    case .vertical:
+                        NSCursor.resizeUpDown.push()
+                    }
+                } else {
+                    NSCursor.pop()
+                }
+            }
+        }
+    }
+}