Solution does not support Live Unit Testing in Visual Studio Enterprise

This is only for developer comfort, not an issue using the SDK itself.

I did try to reproduce this behavior on a clean project, but it seems very specific to the Dapr .NET SDK solution.

## Expected Behavior

When enabling [Live Unit Testing](https://docs.microsoft.com/en-us/visualstudio/test/live-unit-testing-intro) in Visual Studio Enterprise, it should work.

## Actual Behavior

Fails with the message

> [15:40:32.665 Error] System.IO.FileNotFoundException: Could not find file 'D:\github\eNeRGy164\dapr\dotnet-sdk\.vs\all.sln\v16\lut\7304\i\Dapr.Client\netcoreapp3.1\dapr\proto\common\v1\CommonGrpc.cs'.

A normal build generates an empty `CommonGrpc.cs`, but a LUT build apparently does not.
I'm not sure if this is a Visual Studio LUT or a Grpc.Tools bug. Or maybe just the combination of both.

A workaround is to generate the empty file if it is a LUT build.

After this LUT works:

## Steps to Reproduce the Problem

Press _play_ in a Visual Studio Enterprise.

## Release Note

RELEASE NOTE:
**FIX** Support Live Unit Testing in Visual Studio Enterprise.