Update [BindableProperty] Support for Additional Scenarios, Add CommunityToolkit.Maui.SourceGenerators.Internal.UnitTests, Implement [BindableProperty] for Behaviors

[TheCodeTraveler]

Description of Change

As Discussed in our November 2025 Standup, this PR implements the [BindableProperty] attribute, replacing the manually created BindableProperties.

This PR also adds support to [BindableProperty] for the following scenarios:

• Property names using a reserved keyword, e.g. @class
• Properties inside Generic Classes
• Properties inside Nested Classes
• Properties using Nullable reference types
• Properties using Nullable<T>
• Properties using Array types
• Properties inside classes using the global namespace
• Properties inside an inherited class that also has a property using [BindableProperty]
• Multiple Classes in the same file using [BindableProperty]
• All default value types, e.g. bool, char, string and enum

This PR also implements CommunityToolkit.Maui.SourceGenerators.Internal.UnitTests.

PR Checklist

• 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

I've added the breaking change label because the generated code from [BindableProperty] fixes a few typos in BindableProperty names.

[TheCodeTraveler]

It looks very well done. Lets spin up CommunityToolkit.Maui.SourceGenerators.Internal.UnitTests as you suggested and test all the scenarios for Create() and DefaultValue

Thanks @ne0rrmatrix! I've added CommunityToolkit.Maui.SourceGenerators.Internal.UnitTests.

It was a ton of hard work, but I was able to catch a few bugs in the source generator, particularly around edge cases. Thanks to these Unit Tests, the [BindableProperty] now supports all of the following scenarios:

• Property names using a reserved keyword, e.g. @class
• Properties inside Generic Classes
• Properties inside Nested Classes
• Properties using Nullable reference types
• Properties using Nullable<T>
• Properties using Array types
• Properties inside classes using the global namespace
• Properties inside an inherited class that also has a property using [BindableProperty]
• Multiple Classes in the same file using [BindableProperty]
• All default value types, e.g. bool, char, string and enum

[ne0rrmatrix]

This looks like you have thought about just about everything I could want or hope for with this. It is amazing! Approved!