Make registering timeline events easier

As a developer using Glimpse (not an extensions/tab author), I want to make it easier for me to register custom entries in the timeline.

Currently, if I want to register an event, I have to somehow get an instance of the messages bus, create a custom class create own stopwatch or get a hold of the registered `Func<IExecutionTimer>` and then profile the desired code. All of this take a lot more lines of code than it should.

This should be a one liner for moment in time events or a simple using statement if its a duration event. Any solution probably should be able to be accessed statically and a null provider registered in this hook so that the code works for testing, but when my code fully runs, it uses a real provider.