Alert UI component doesn't support reactive bindings

[Al12rs]

Bug Report

Summary

Our Alert.xaml.cs component doesn't support reactive bindings for Title and Body properties.
These can only be set using normal or compiled bindings from the view.

Details

This is caused by OnApplyTemplate() hiding parts of the template depending on the state of the properties (e.g. with IsNullOrEmpty()).
This happens when the template is first applied, meaning that the bindings from the code behind have not been setup yet (they happen on WhenActivated).

What is the expected behaviour?

If a binding is setup for the contents of the Title or the Body, Alert should set those sections of the template to visible upon set.