Add SpacingLayout support (#602)

Author: Kyle-Ye

Sources/OpenSwiftUICore/Layout/SpacingLayout.swift

@@ -0,0 +1,34 @@
+//
+//  SpacingLayout.swift
+//  OpenSwiftUICore
+//
+//  Audited for 6.5.4
+//  Status: Complete
+
+import OpenCoreGraphicsShims
+
+struct SpacingLayout: UnaryLayout {
+    var spacing: Spacing
+
+    func spacing(in context: SizeAndSpacingContext, child: LayoutProxy) -> Spacing {
+        spacing
+    }
+
+    func placement(of child: LayoutProxy, in context: PlacementContext) -> _Placement {
+        _Placement(
+            proposedSize: context.proposedSize,
+            aligning: .center,
+            in: context.size
+        )
+    }
+
+    func sizeThatFits(in proposedSize: _ProposedSize, context: SizeAndSpacingContext, child: LayoutProxy) -> CGSize {
+        child.size(in: proposedSize)
+    }
+}
+
+extension View {
+    package func spacing(_ spacing: Spacing) -> some View {
+        modifier(SpacingLayout(spacing: spacing))
+    }
+}