Add Attached Bindable Property support

[ne0rrmatrix]

Description of Change

Add support for Attached Bindable Properties so that we can update and merge #3016 #3000

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

Additional information

This add support for both CreateAttached and Readonly support. Link to documentation for Attached Properties https://learn.microsoft.com/en-us/dotnet/maui/fundamentals/attached-properties?view=net-maui-10.0

[TheCodeTraveler]

Hey James! It looks like you don't have an in-depth understanding on Attached Bindable Properties.

They are a BindableProperty that don't have an associated public property. Instead, they are accessed via static methods.

From from the docs:

...attached properties enable an object to assign a value for a property that its own class doesn't define

Here's an example from the docs:

public class MyControl
{
    public static readonly BindableProperty HasShadowProperty =
        BindableProperty.CreateAttached("HasShadow", typeof(bool), typeof(MyControl), false);

    public static bool GetHasShadow(BindableObject view)
    {
        return (bool)view.GetValue (HasShadowProperty);
    }

    public static void SetHasShadow(BindableObject view, bool value)
    {
        view.SetValue(HasShadowProperty, value);
    } 

}

Therefore, we won't be placing [AttachedBindableProperty] on a property.

Options For [AttachedBindableProperty]

1. Attribute on Class

We can place the attribute on the class:

[AttachedBindableProperty<bool>(PropertyName="HasShadow", DefaultValue = false, BindingMode = BindingMode.OneWay, ValidateValueMethodName = null, PropertyChangedMethodName = null, PropertyChangingMethodName = null, CoerceValueMethodName = null, DefaultValueCreatorMethodName = null)]
public partial class MyCustomView
{
}

2. Attribute on Constructor

We can place the attribute on the constructor

public partial class MyCustomView
{
    [AttachedBindableProperty<bool>(PropertyName="HasShadow", DefaultValue = false, BindingMode = BindingMode.OneWay, ValidateValueMethodName = null, PropertyChangedMethodName = null, PropertyChangingMethodName = null, CoerceValueMethodName = null, DefaultValueCreatorMethodName = null)]
    public class MyCustomView()
    {

    }
}

You've clearly invested a lot of time into this. I highly recommend you do more research on Attached BindableProperty to understand their use and look at examples of how developers use them before devoting more time towards writing this source generator:

https://learn.microsoft.com/en-us/dotnet/maui/fundamentals/attached-properties?view=net-maui-10.0

https://learn.microsoft.com/en-us/dotnet/api/microsoft.maui.controls.bindableproperty.createattached?view=net-maui-10.0