added System.Composition binding redirects to omnisharp.exe

[filipw]

Follow up to #930
At the moment if you start Omnisharp, and you have a folder with external code actions configured, it will fail to start:

C:\code\omnisharp-roslyn>"C:\code\omnisharp-roslyn\artifacts\publish\OmniSharp\default\net46\OmniSharp.exe" -s C:\code\omnisharp-roslyn\src\OmniSharp --stdio
OmniSharp: -s C:\code\omnisharp-roslyn\src\OmniSharp --stdio
System.IO.FileNotFoundException: Could not load file or assembly 'System.Composition.AttributedModel, Version=1.0.27.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a' or one of its dependencies. The system cannot find the file specified.
File name: 'System.Composition.AttributedModel, Version=1.0.27.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'
   at System.ModuleHandle.ResolveType(RuntimeModule module, Int32 typeToken, IntPtr* typeInstArgs, Int32 typeInstCount, IntPtr* methodInstArgs, Int32 methodInstCount, ObjectHandleOnStack type)
   at System.ModuleHandle.ResolveTypeHandleInternal(RuntimeModule module, Int32 typeToken, RuntimeTypeHandle[] typeInstantiationContext, RuntimeTypeHandle[] methodInstantiationContext)
   at System.Reflection.RuntimeModule.ResolveType(Int32 metadataToken, Type[] genericTypeArguments, Type[] genericMethodArguments)
   at System.Reflection.CustomAttribute.FilterCustomAttributeRecord(CustomAttributeRecord caRecord, MetadataImport scope, Assembly& lastAptcaOkAssembly, RuntimeModule decoratedModule, MetadataToken decoratedToken, RuntimeType attributeFilterType, Boolean mustBeInheritable, Object[] attributes, IList derivedAttributes, RuntimeType& attributeType, IRuntimeMethodInfo& ctor, Boolean& ctorHasParameters, Boolean& isVarArg)
   at System.Reflection.CustomAttribute.GetCustomAttributes(RuntimeModule decoratedModule, Int32 decoratedMetadataToken, Int32 pcaCount, RuntimeType attributeFilterType, Boolean mustBeInheritable, IList derivedAttributes, Boolean isDecoratedTargetSecurityTransparent)

There is a unit test for this https://github.com/OmniSharp/omnisharp-roslyn/blob/master/tests/OmniSharp.Roslyn.CSharp.Tests/CodeActionsV2Facts.cs#L39 but it didn't catch this because the test project has the necessary binding redirects 🙂

[DustinCampbell]

Could've sworn we had these.