private dependency-property raises errors in the logs

[Xiaoy312]

Current behavior

dependency property with private get/setter and dp backing-field is raising errors in the logs when the owning control are used in another assembly/app:

fail: Uno.UI.DataBinding.BindingPropertyHelper[0]
      The [VerticalMaxScroll] property getter does not exist on type [Uno.Toolkit.UI.ZoomContentControl]
fail: Uno.UI.DataBinding.BindingPropertyHelper[0]
      The [VerticalMinScroll] property getter does not exist on type [Uno.Toolkit.UI.ZoomContentControl]
fail: Uno.UI.DataBinding.BindingPropertyHelper[0]
      The [VerticalScrollValue] property getter does not exist on type [Uno.Toolkit.UI.ZoomContentControl]
fail: Uno.UI.DataBinding.BindingPropertyHelper[0]
      The [HorizontalMaxScroll] property getter does not exist on type [Uno.Toolkit.UI.ZoomContentControl]
fail: Uno.UI.DataBinding.BindingPropertyHelper[0]
      The [HorizontalMinScroll] property getter does not exist on type [Uno.Toolkit.UI.ZoomContentControl]
fail: Uno.UI.DataBinding.BindingPropertyHelper[0]
      The [HorizontalScrollValue] property getter does not exist on type [Uno.Toolkit.UI.ZoomContentControl]

as seen on: https://github.com/unoplatform/uno.hotdesign/pull/5175#issuecomment-3444315730

Expected behavior

no error

How to reproduce it (as minimally and precisely as possible)

...

Anything else we need to know?