ActionExtension for events does not respect guard proeprty

From wiki:
>The syntax is exactly the same, although there's no concept of a guard property here.

Why? I want to be able to set `MouseLeftButtonUp="{s:Action SomeAction}"` and only have the handler actually execute when the guard property lets it. The justification is that I want to be able to use events in the same way I use commands, without having to use some kind of `EventToCommand` contraption.

Start by tracing ActionExtension for event handling and how the guard property is evaluated for commands. Reproduce the MouseLeftButtonUp example, then verify that the event handler executes only when the guard property allows it, without requiring EventToCommand.

Written by the indexing model from the issue text.