Fix UseToStringAsLabel on SubclassSelector attribute

[jhodk]

Description

I am using unity editor version 6000.3.7f1.
The property UseToStringAsLabel on the SubclassSelector attribute does not currently appear to have any impact on the GUI render.

According to this code on the current main branch, we would expect the foodThree example field to be rendered in the editor with label "Grape".

Unity-SerializeReferenceExtensions/Assets/Example/Example.cs

Lines 73 to 75 in e23441e

	// UseToStringAsLabel support on UNITY_2021_3_OR_NEWER
	[SerializeReference, SubclassSelector(UseToStringAsLabel = true)]
	public Food foodThree = new Grape();

However the left side of the screenshot below shows that is not the case - the name remains as "Food Three".

Changes made

• Moved EditorGUI.BeginProperty calls after the label.text override.
• Added ToString override in Food example class
• Added list Foods Three to Example script with UseToStringAsLabel = true

Screenshots

Left is before the fix, Right is after the fix

Thanks.