MultipleX and MultipleY are missing the ConstraintPropertyChanged callback

[sylveon]

Describe the bug

The MultipleX and MultipleY dependency properties on ConstrainedBox do not register the ConstraintPropertyChanged callback, meaning that if they are changed, the layout isn't updated until something else invalidates it

• Is this bug a regression in the toolkit? No

For example ScaleY:

WindowsCommunityToolkit/Microsoft.Toolkit.Uwp.UI.Controls.Primitives/ConstrainedBox/ConstrainedBox.Properties.cs

Lines 48 to 49 in ee93385

	public static readonly DependencyProperty ScaleYProperty =
	DependencyProperty.Register(nameof(ScaleY), typeof(double), typeof(ConstrainedBox), new PropertyMetadata(1.0, ConstraintPropertyChanged));

Compared to MultipleY:

WindowsCommunityToolkit/Microsoft.Toolkit.Uwp.UI.Controls.Primitives/ConstrainedBox/ConstrainedBox.Properties.cs

Lines 78 to 79 in ee93385

	public static readonly DependencyProperty MultipleYProperty =
	DependencyProperty.Register(nameof(MultipleY), typeof(int), typeof(ConstrainedBox), new PropertyMetadata(null));

Steps to Reproduce

• Can this be reproduced in the Sample App? (Either in a sample as-is or with new XAML pasted in the editor.) If so, please provide custom XAML or steps to reproduce. If not, let us know why it can't be reproduced (e.g. more complex setup, environment, dependencies, etc...)

Steps to reproduce the behavior:

1. Use the constrained box control somewhere.
2. Modify MultipleX or MultipleY at runtime.
3. Observe that changes do not apply until a manual layout invalidation.

Expected behavior

The changes should apply instantly

Screenshots

N/A

Environment

N/A, bug found while reading the source code.

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