Fix NullReferenceException when EditorField uses implicit Style with FontFamily

[Copilot]

EditorField crashes with NullReferenceException when FontFamily is set via implicit style. The property callback attempts to access labelTitle and EditorView before control template application during construction.

Changes

• EditorField.BindableProperties.cs: Add null checks in FontFamilyProperty callback before accessing EditorView and labelTitle
• InputField.cs: Add null check in FontAutoScalingEnabledProperty callback before accessing labelTitle (same root cause)
• EditorField_Test.cs: Add test coverage for implicit style application and direct property setting

Example

Before this fix, the following XAML would crash on initialization:

<Style TargetType="material:EditorField">
    <Setter Property="FontFamily" Value="OpenSansSemibold" />
</Style>

The callback now defers property application until the visual tree elements exist:

if (editorField.EditorView != null)
{
    editorField.EditorView.FontFamily = (string)newValue;
}

if (editorField.labelTitle != null)
{
    editorField.labelTitle.FontFamily = (string)newValue;
}

Original prompt

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This section details on the original issue you should resolve

<issue_title>NullReferenceException when EditorField uses a implicit Style with FontFamily</issue_title>
<issue_description>### Summary
A NullReferenceException occurs during control initialization when an implicit Style targeting material:EditorField defines the FontFamily property.
The exception is thrown while styles are being applied, before any user interaction.

Affected Versions

• UraniumUI: 2.14.0 (last known working version: 2.9.1)

Steps to Reproduce

1. Define an implicit style for material:EditorField in Styles.xaml that sets FontFamily
2. Instantiate an EditorField in any page
3. Run the application

A minimal reproduction is available here:
https://github.com/idenardi/uraniumui-editorfield-style

Style Example

<Style TargetType="material:EditorField">
    <Setter Property="FontFamily" Value="OpenSansSemibold" />
</Style>

Actual Behavior

The application crashes with a NullReferenceException during EditorField initialization.

Stacktrace (partial)

System.NullReferenceException: Object reference not set to an instance of an object
   at UraniumUI.Material.Controls.EditorField.<>c.<.cctor>b__64_1(...)
   at Microsoft.Maui.Controls.Setter.Apply(...)
   at Microsoft.Maui.Controls.Style.ApplyCore(...)
   ...
   at UraniumUI.Material.Controls.EditorField..ctor()

Workaround

Removing the FontFamily setter from the implicit EditorField style prevents the crash.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes NullReferenceException when EditorField uses a implicit Style with FontFamily #934

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