Make FrameworkElement.Triggers support more types of triggers

`FrameworkElement.Triggers` now only accepts `EventTriggers` type, and we have to write a `Style` to add other triggers to the element, as shown below:

```xml



<Style.Triggers>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Background" Value="Gray" />
</Trigger>
</Style.Triggers>



```

I think we need a more simplified xaml syntax to add triggers (`Trigger`, `DataTrigger`, `MultiTrigger` and `MultiDataTrigger`), just like below:

```xml







```