Make method public to use in Avalonia

Author: wieslawsoltes

src/Microsoft.DotNet.Wpf/src/System.Xaml/System/Xaml/XamlSchemaContext.cs

@@ -646,7 +646,7 @@ protected internal XamlValueConverter<TConverterBase> GetValueConverter<TConvert
  return (XamlValueConverter<TConverterBase>)result;
  }
 
- internal virtual XamlMember GetProperty(PropertyInfo pi)
+ public virtual XamlMember GetProperty(PropertyInfo pi)
  {
  var xpik = new ReferenceEqualityTuple<MemberInfo, MemberInfo>(pi, null);
  XamlMember member;
@@ -671,7 +671,7 @@ internal virtual XamlMember GetEvent(EventInfo ei)
  }
 
  // Caller responsible for ensuring getter and setter not null
- internal virtual XamlMember GetAttachableProperty(string name, MethodInfo getter, MethodInfo setter)
+ public virtual XamlMember GetAttachableProperty(string name, MethodInfo getter, MethodInfo setter)
  {
  XamlMember property;
  var xpik = new ReferenceEqualityTuple<MemberInfo, MemberInfo>(getter, setter);