Add overrides to Help with Obsoleting Compatibility.Layout

[PureWeen]

Description of Change

We had a few vendors test out the follow PR #29281 and they reported crashes on OnSizeAllocated.

An unhandled exception of type 'System.MethodAccessException' occurred in Microsoft.MacCatalyst.dll: 'Method `Microsoft.Maui.Controls.Compatibility.Layout.OnSizeAllocated(double,double)' is inaccessible from method

If we add these overrides to the base classes that we are keeping and then 3rd parties recompile, that will better prepare us down the road for hopefully getting to delete Compatibility.Layout

[Copilot]

Pull Request Overview

This PR adds protected overrides of OnSizeAllocated to maintain binary compatibility with existing consumers when Compatibility.Layout is removed.

• Introduces OnSizeAllocated overrides in TemplatedView, ScrollView, and ContentPresenter
• Updates PublicAPI.Unshipped files to expose the new overrides
• Ensures future binary compatibility with libraries compiled against MAUI

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 5 comments.

File	Description
src/Controls/src/Core/TemplatedView/TemplatedView.cs	Added OnSizeAllocated override and compatibility comments
src/Controls/src/Core/ScrollView/ScrollView.cs	Added OnSizeAllocated override and compatibility comments
src/Controls/src/Core/ContentPresenter.cs	Added OnSizeAllocated override and compatibility comments
src/Controls/src/Core/PublicAPI/*/PublicAPI.Unshipped.txt	Exposed the new overrides in all target frameworks' unshipped APIs

Comments suppressed due to low confidence (1)

src/Controls/src/Core/TemplatedView/TemplatedView.cs:146

• There are no existing tests covering the new OnSizeAllocated override. Please add or update test cases in TestCases.Shared.Tests and TestCases.HostApp to verify this method is invoked correctly.

		protected override void OnSizeAllocated(double width, double height)