Refactor Layouts to use [BindableProperty] partial properties

[ne0rrmatrix]

Description of Change

This adds support for [BindableProperties] to Layouts in CommunityToolkitMaui.
This PR is blocked until support is added for BindableProperties.AddAttached as it is required to complete this PR. There are several classes StateContainer, StateContainerController and StateView that require addition updates to our internal source generator to complete this.

• Fixes #

PR Checklist

• Has a linked Issue, and the Issue has been approved(bug) or Championed (feature/proposal)
• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard
• Documentation created or updated: https://github.com/MicrosoftDocs/CommunityToolkit/pulls

Additional information

Blocked until support for Attached bindable properties is added.

[TheCodeTraveler]

Thanks James!

Could you also please create a [ClassName]Defaults.shared.cs class for each of these Views in CommunityToolkit.Maui.Core/Defaults/ and also add a Unit Test for each called EnsureDefaults that verifies the default value for each property in the class equals the expected default value?

Here's an example that I added for FadeAnimation in the recent PR:

Maui/src/CommunityToolkit.Maui.Core/Primitives/Defaults/FadeAnimationDefaults.shared.cs

Lines 3 to 7 in f5b68d3

	static class FadeAnimationDefaults
	{
	public const uint Length = 300u;
	public const double Opacity = 0.3;
	}

Maui/src/CommunityToolkit.Maui.UnitTests/Animations/FadeAnimationTests.cs

Lines 72 to 82 in 8bd0af3

	[Fact]
	public void EnsureDefaults()
	{
	// Arrange
	var animation = new FadeAnimation();
	// Act // Assert
	Assert.Equal(BaseAnimationDefaults.Easing, animation.Easing);
	Assert.Equal(FadeAnimationDefaults.Length, animation.Length);
	Assert.Equal(FadeAnimationDefaults.Opacity, animation.Opacity);
	}

We should've created [ClassName]Defaults.shared.cs and implemented these Unit Tests when originally creating every control in CommunityToolkit.Maui. But now that we're going back and editing every control to implement [BindableProperty], I've found that this is a great time to clean up our codebase and implement these!

[ne0rrmatrix]

Thanks James!

Could you also please create a [ClassName]Defaults.shared.cs class for each of these Views in CommunityToolkit.Maui.Core/Defaults/ and also add a Unit Test for each called EnsureDefaults that verifies the default value for each property in the class equals the expected default value?

Here's an example that I added for FadeAnimation in the recent PR:

Maui/src/CommunityToolkit.Maui.Core/Primitives/Defaults/FadeAnimationDefaults.shared.cs

Lines 3 to 7 in f5b68d3

	static class FadeAnimationDefaults
	{
	public const uint Length = 300u;
	public const double Opacity = 0.3;
	}

Maui/src/CommunityToolkit.Maui.UnitTests/Animations/FadeAnimationTests.cs

Lines 72 to 82 in 8bd0af3

	[Fact]
	public void EnsureDefaults()
	{
	// Arrange
	var animation = new FadeAnimation();
	// Act // Assert
	Assert.Equal(BaseAnimationDefaults.Easing, animation.Easing);
	Assert.Equal(FadeAnimationDefaults.Length, animation.Length);
	Assert.Equal(FadeAnimationDefaults.Opacity, animation.Opacity);
	}

We should've created [ClassName]Defaults.shared.cs and implemented these Unit Tests when originally creating every control in CommunityToolkit.Maui. But now that we're going back and editing every control to implement [BindableProperty], I've found that this is a great time to clean up our codebase and implement these!

Sounds like a plan. I will make the requested changes.

[Copilot]

Pull request overview

This PR refactors two layout classes (UniformItemsLayout and DockLayout) to use modern [BindableProperty] partial properties instead of traditional BindableProperty definitions. The refactoring introduces default value constants in new static classes and adds unit tests to verify default values are correctly set.

Key changes:

• Migrates bindable properties to use source-generated partial properties with [BindableProperty] attributes
• Extracts default values into centralized UniformItemLayoutDefaults and DockLayoutDefaults classes
• Adds unit tests to validate default property values

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 10 comments.

Show a summary per file

File	Description
UniformItemsLayout.shared.cs	Refactored MaxRows and MaxColumns properties to use [BindableProperty] with partial properties; moved validation to property changed callbacks
DockLayout.shared.cs	Refactored ShouldExpandLastChild, HorizontalSpacing, and VerticalSpacing properties to use [BindableProperty] with partial properties
UniformItemLayoutDefaults.shared.cs	New static class defining default constants for UniformItemsLayout properties
DockLayoutDefaults.shared.cs	New static class defining default constants for DockLayout properties
UniformItemsLayoutTests.cs	Added test to verify default property values; added necessary namespace import
DockLayoutTests.cs	Added test to verify default property values

[Copilot]

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[TheCodeTraveler]

Thanks James! Let's go ahead and merge this.

I've included the Attached Bindable Property updates for DockLayout in my [AttachedBindableProperty] PR: #3024