[NET10] Make `VisualElement.ComputeConstraintForView` and `LayoutConstraint` enum public

[albyrock87]

Description

Enable custom layouts to specify whether a given child is being constrained on a fixed size.

Public API Changes

• Make ComputeConstraintForView just protected virtual
  

  maui/src/Controls/src/Core/VisualElement/VisualElement.cs

  Lines 1386 to 1388 in d988ddf

  	internal virtual void ComputeConstraintForView(View view) => view.ComputedConstraint = LayoutConstraint.None;

• Make LayoutConstraint public
  

  maui/src/Controls/src/Core/LayoutConstraint.cs

  Lines 6 to 12 in d988ddf

  	internal enum LayoutConstraint
  	{
  	None = 0,
  	HorizontallyFixed = 1 << 0,
  	VerticallyFixed = 1 << 1,
  	Fixed = HorizontallyFixed | VerticallyFixed
  	}

Intended Use-Case

In MAUI it's super easy to build new custom layouts, and sometimes layout may constrain a given children on the horizontal or vertical axis, so that even when the measure of that child changes, there's no need to invalidate the entire hierarchy.

This could enable MAUI to highly reduce the number of layout passes.
A step in this direction has been made on #28479 and #28756, where on the latter we moved ComputeConstraintForView call to VisualElement measure invalidation.