Use expression trees for all type-safe remote calls (💥 BREAKING CHANGES)

[cretz]

What was changed

We have removed the concept of "Ref" and replaced with expression trees. Primary reasons:

• "Ref" approach was too unfamiliar to .NET devs
• "Ref" approach required implementers to add something when they implemented
• Expression trees are more familiar even if they have slight shortcomings (e.g. performance of interpreting complex arg expressions and not everything like optional/named parameters accepted)
• Expression trees allow for fewer overloads to support 0, 1, N-arg calls
• Expression trees allow us to store the type of workflow on the workflow handle, child workflow handle, and external workflow handle allowing us to enforce that type-safe signal and query calls are on the same workflow

💥 BREAKING CHANGES:

The following calls were changed to support expression trees instead of "Ref":

• Temporalio.Client.ITemporalClient.ExecuteWorkflowAsync (extension)
• Temporalio.Client.ITemporalClient.StartWorkflowAsync
• Temporalio.Client.Schedules.ScheduleActionStartWorkflow.Create
• Temporalio.Client.WorkflowHandle.QueryAsync
• Temporalio.Client.WorkflowHandle.SignalAsync
• Temporalio.Workflows.ChildWorkflowHandle.SignalAsync
• Temporalio.Workflows.ExternalWorkflowHandle.SignalAsync
• Temporalio.Workflows.Workflow.CreateContinueAsNewException
• Temporalio.Workflows.Workflow.ExecuteActivityAsync
• Temporalio.Workflows.Workflow.ExecuteChildWorkflowAsync
• Temporalio.Workflows.Workflow.ExecuteLocalActivityAsync
• Temporalio.Workflows.Workflow.StartChildWorkflowAsync

Any previous use of these is now likely as compiler error. To get an idea of what the changes look like from a caller POV, see the tests/Temporalio.Tests/Worker/WorkflowWorkerTests.cs file.

Checklist

1. Closes [Feature Request] Change Ref approach to expression-based #62

[cretz]

Note, in a subsequent PR, I will be moving all Temporalio top-namespace-level types to Temporalio.Common, this just happens to be the first

[bergundy]

Skimmed this, overall LGTM