[Feature Request] Re-investigate signals/queries/activities as properties

[Chad Retz]

Describe the solution you'd like

We initially didn't allow signals or queries as properties because we required delegates to invoke them. But now that we're using expressions we probably can. Specifically, we may want to support:

• [WorkflowSignal] on properties with setters where the setter is invoked for the signal
• [WorkflowQuery] on properties where the getter is invoked for the query

When [WorkflowUpdate] comes around, setting it on a property will invoke the setter and return the getter

[Chad Retz]

Even activities can be properties

[Chad Retz]

So we can't do signals because .NET lambda expression trees don't support assignment operators. And there's not a good reason to support activities as property getters at this time (should be clear they are methods). But workflow queries make plenty of sense as properties.