[NET10] Make VisualElement.ComputeConstraintForView and LayoutConstraint enum public

[jsuarezruiz]

Description of Change

This PR enhances MAUI's custom layout capabilities by refining constraint handling for child elements. Specifically:

• Makes ComputeConstraintForView protected virtual, allowing custom layouts to override it if needed.
• Changes LayoutConstraint to public, so developers can better manage layout constraints when measuring child elements.

These adjustments will help reduce unnecessary layout passes.

Issues Fixed

Fixes #28897

[Copilot]

Pull Request Overview

This PR refines MAUI’s custom layout capabilities by adjusting constraint handling for child elements. The key changes include:

• Changing the access modifier of ComputeConstraintForView from internal to protected virtual so that custom layouts can override it.
• Making the LayoutConstraint enum public for enhanced layout constraint management.
• Updating relevant PublicAPI files to expose the new public API changes.

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 1 comment.

File	Description
src/Controls/src/Core/VisualElement/VisualElement.cs	Changed ComputeConstraintForView’s access modifier to protected virtual
src/Controls/src/Core/LayoutConstraint.cs	Changed LayoutConstraint from internal to public
PublicAPI.Unshipped.txt (all platforms)	Exposed LayoutConstraint and updated ComputeConstraintForView signature in the public API

Comments suppressed due to low confidence (2)

src/Controls/src/Core/LayoutConstraint.cs:6

• Ensure that the public documentation in the docs folder is updated to reflect the new public access of LayoutConstraint and its intended usage.

public enum LayoutConstraint

src/Controls/src/Core/PublicAPI/netstandard/PublicAPI.Unshipped.txt:313

• The public API signature for ComputeConstraintForView has been updated. Please confirm that this potential breaking change is acceptable and that versioning/documentation adjustments are in place.

+~virtual Microsoft.Maui.Controls.VisualElement.ComputeConstraintForView(Microsoft.Maui.Controls.View view) -> void