[iOS, Mac] Fix for StackLayout not respecting explicit size on iOS and MacCatalyst

[HarishwaranVijayakumar]

Note

Are you waiting for the changes in this PR to be merged?
It would be very helpful if you could test the resulting artifacts from this PR and let us know in a comment if this change resolves your issue. Thank you!

Issue Details

• When adding a label inside a fixed-width VerticalStackLayout, the label appears to be cropped and is not fully visible.

Root Cause of the issue

• The explicit WidthRequest was not properly considered during layout measurement. As a result, iOS and MacCatalyst did not respect the fixed width constraint, causing the label to not be fully visible.

Description of Change

• Updated HorizontalStackLayoutManager and VerticalStackLayoutManager to use explicit Width and Height properties of the stack layout when set, instead of the passed constraints, during measurement calculations. This ensures layouts behave as expected when explicit dimensions are provided.

Issues Fixed

Fixes #14200
Fixes #18450

Tested the behaviour in the following platforms

• - Windows
• - Android
• - iOS
• - Mac

Output

Before	After

[dotnet-policy-service]

Hey there @@HarishwaranVijayakumar! Thank you so much for your PR! Someone from the team will get assigned to your PR shortly and we'll get it reviewed.

[jsuarezruiz]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 3 pipeline(s).

[jsuarezruiz]

This is duplicated, could consider extracting to a helper method:

private (double width, double height) GetEffectiveConstraints(
    double widthConstraint, 
    double heightConstraint)
{
    return (
        Dimension.IsExplicitSet(Stack.Width) ? Stack.Width : widthConstraint,
        Dimension.IsExplicitSet(Stack.Height) ? Stack.Height : heightConstraint
    );
}

[jsuarezruiz]

Consider adding a test for HorizontalStackLayout with explicit HeightRequest