Add constrainedSize modifier

Summary:
Adds a new constrainedSize(maxWidth:maxHeight:) modifier to QuickLayout that clamps the parent's proposed size before measuring the child.

Unlike .frame(maxWidth:maxHeight:) (FlexibleFrame), this modifier does not create an invisible frame around the child or reposition it with alignment. It simply constrains the proposed size passed to the child and reports the child's actual size as its own. This makes it useful when you want to limit how much space a child is offered without introducing extra layout space around it.

The new ConstrainedSizeElement is modeled after FixedFrameElement but differs in three key ways:

Reports the child's actual size rather than the frame's size
Delegates flexibility to the child instead of reporting .fixedSize
Does not perform alignment positioning — the child is placed at the origin

Reviewed By: xavierjurado

Differential Revision: D94706249

fbshipit-source-id: 26f6a505c64a65964478d2c915962b9bc37c1b6c

Author: constantine-fry

Sources/QuickLayout/QuickLayoutBridge/QuickLayout.swift

@@ -195,6 +195,14 @@ public extension Element {
     FixedSizeElement(child: self, horizontal: axis.contains(.horizontal), vertical: axis.contains(.vertical))
   }
 
+  /// Clamps the parent's proposed size to the specified constraints and
+  /// acquires the child's actual size as its own.
+  /// Similar to Flexible Frame with maxWidth and maxHeight, but does not
+  /// leave an invisible space around the child view.
+  func constrainedSize(maxWidth: CGFloat? = nil, maxHeight: CGFloat? = nil) -> Element & Layout {
+    ConstrainedSizeElement(child: self, maxWidth: maxWidth, maxHeight: maxHeight)
+  }
+
   /// Sets the priority by which a parent V/HStack should allocate space to this child.
   /// A view's default priority is 0, which distributes available space evenly to all sibling views.
   /// Set a higher priority to measure the view first with a larger portion of available space.