## Workflow checksums changed from MD5 to SHA1

### Scope
Minor

### Version Introduced
4.7

### Source Analyzer Status
NotPlanned

### Change Description
To support debugging with Visual Studio, 
the Workflow runtime generates a checksum for a workflow instance using a hashing algorithm.
In the .NET Framework 4.6.2 and earlier versions, workflow checksum hashing used the MD5 
algorithm, which caused issues on FIPS-enabled systems. Starting with the .NET Framework 4.7, 
the algorithm is SHA1. If your code has persisted these checksums, they will be incompatible. 

- [x] Quirked 
- [ ] Build-time break 

### Recommended Action
If your code is unable to load workflow instances due to a checksum failure, try setting 
the `AppContext` switch "Switch.System.Activities.UseMD5ForWFDebugger" to true.

In code:
```csharp
System.AppContext.SetSwitch("Switch.System.Activities.UseMD5ForWFDebugger", true);
```

Or in configuration:
```xml
<configuration>
   <runtime>
      <AppContextSwitchOverrides value="Switch.System.Activities.UseMD5ForWFDebugger=true" /> 
   </runtime>
</configuration>
```

### Affected APIs
* Not detectable via API analysis

### Category
Windows Workflow Foundation (WF)

<!-- breaking change id: 176 -->