Update HVStackLayout documentation

Sources/OpenSwiftUI/Layout/LayoutFundamentals/Stack/HVStackLayout.swift

@@ -1,33 +1,59 @@
 import Foundation
 
+/// A layout that arranges its children in a horizontal line.
 @frozen
 public struct _HStackLayout {
+    /// The vertical alignment of children.
     public var alignment: VerticalAlignment
+
+    /// The distance between adjacent children, or `nil` if the stack should
+    /// choose a default distance for each pair of children.
     public var spacing: CGFloat?
 
+    /// Creates an instance with the given spacing and vertical alignment.
+    ///
+    /// - Parameters:
+    ///     - alignment: The guide for aligning the subviews in this stack. It
+    ///     has the same vertical screen coordinate for all children.
+    ///     - spacing: The distance between adjacent subviews, or `nil` if you
+    ///     want the stack to choose a default distance for each pair of
+    ///     subviews.
     @inlinable
     public init(alignment: VerticalAlignment = .center, spacing: CGFloat? = nil) {
         self.alignment = alignment
         self.spacing = spacing
     }
 
     public typealias AnimatableData = EmptyAnimatableData
-    public typealias Body = Swift.Never
+    public typealias Body = Never
 }
 
+/// A layout that arranges its children in a vertical line.
 @frozen
 public struct _VStackLayout {
+    /// The horizontal alignment of children.
     public var alignment: HorizontalAlignment
+
+    /// The distance between adjacent children, or `nil` if the stack should
+    /// choose a default distance for each pair of children.
     public var spacing: CGFloat?
 
+    /// Creates an instance with the given spacing and horizontal alignment.
+    ///
+    /// - Parameters:
+    ///     - alignment: The guide for aligning the subviews in this stack. It
+    ///     has the same horizontal screen coordinate for all children.
+    ///     - spacing: The distance between adjacent subviews, or `nil` if you
+    ///     want the stack to choose a default distance for each pair of
+    ///     subviews.
     @inlinable
     public init(alignment: HorizontalAlignment = .center, spacing: CGFloat? = nil) {
         self.alignment = alignment
         self.spacing = spacing
     }
 
     public typealias AnimatableData = EmptyAnimatableData
-    public typealias Body = Swift.Never
+    public typealias Body = Never
 }
 
 extension _HStackLayout: _VariadicView_ImplicitRoot {