[XSG] Fix Style Setters referencing source-generated bindable properties

[simonrozsival]

Description

Fixes an issue where using source-generated bindable properties (created via [BindableProperty] attribute) in Style Setters would cause the XAML source generator to fail with error MAUIG1001: The method or operation is not implemented.

Problem

When a Style Setter references a source-generated bindable property, GetBindableProperty() returns null because the property field symbol is not available the same way as for manually-defined bindable properties. The code then called bpRef.ToFQDisplayString() on a null reference, causing the failure.

Example XAML that failed:

<Style x:Key="MyLabelStyle" TargetType="local:MyLabel">
    <Setter Property="MyProperty" Value="Bar" />
</Style>

Where MyProperty is defined as:

public partial class MyLabel : Label
{
    [BindableProperty]
    public partial string MyProperty { get; set; }
}

Solution

Added a fallback mechanism in SetterValueProvider that:

1. When GetBindableProperty() returns null, parses the property name from the Setter's Property attribute
2. Resolves the target type from the parent Style/Trigger element
3. Uses HasBindablePropertyHeuristic to verify a bindable property exists
4. Constructs the fully-qualified property reference directly (e.g., global::Namespace.MyLabel.MyPropertyProperty)

Testing

• All 147 source generator unit tests pass
• Verified with repro project that previously failed now builds successfully and generates correct code

[Copilot]

Pull request overview

Copilot reviewed 1 out of 1 changed files in this pull request and generated 6 comments.

[simonrozsival]

/azp run maui-pr-uitests

[azure-pipelines]

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