Add WriteCodeFragment build task (dotnet#3702)

* add WriteCodeFragment build task for assembly-level attribute generation

* move InternalsVisibleTo to the project files where possible

Author: brettfo

Common/AssemblyInfo.fs

@@ -4,10 +4,6 @@ namespace Microsoft.VisualStudio.FSharp.Editor
 
 open Microsoft.VisualStudio.Shell
 
-[<assembly:System.Runtime.CompilerServices.InternalsVisibleTo("FSharp.ProjectSystem.FSharp, PublicKey=002400000480000094000000060200000024000052534131000400000100010007D1FA57C4AED9F0A32E84AA0FAEFD0DE9E8FD6AEC8F87FB03766C834C99921EB23BE79AD9D5DCC1DD9AD236132102900B723CF980957FC4E177108FC607774F29E8320E92EA05ECE4E821C0A5EFE8F1645C4C0C93C1AB99285D622CAA652C1DFAD63D745D6F2DE5F17E5EAF0FC4963D261C8A12436518206DC093344D5AD293")>]
-[<assembly:System.Runtime.CompilerServices.InternalsVisibleTo("VisualFSharp.Unittests, PublicKey=002400000480000094000000060200000024000052534131000400000100010007D1FA57C4AED9F0A32E84AA0FAEFD0DE9E8FD6AEC8F87FB03766C834C99921EB23BE79AD9D5DCC1DD9AD236132102900B723CF980957FC4E177108FC607774F29E8320E92EA05ECE4E821C0A5EFE8F1645C4C0C93C1AB99285D622CAA652C1DFAD63D745D6F2DE5F17E5EAF0FC4963D261C8A12436518206DC093344D5AD293")>]
-[<assembly:System.Runtime.CompilerServices.InternalsVisibleTo("VisualFSharp.Salsa, PublicKey=002400000480000094000000060200000024000052534131000400000100010007D1FA57C4AED9F0A32E84AA0FAEFD0DE9E8FD6AEC8F87FB03766C834C99921EB23BE79AD9D5DCC1DD9AD236132102900B723CF980957FC4E177108FC607774F29E8320E92EA05ECE4E821C0A5EFE8F1645C4C0C93C1AB99285D622CAA652C1DFAD63D745D6F2DE5F17E5EAF0FC4963D261C8A12436518206DC093344D5AD293")>]
-
 [<assembly: ProvideCodeBase(CodeBase = @"$PackageFolder$\FSharp.Editor.dll")>]
 [<assembly: ProvideCodeBase(CodeBase = @"$PackageFolder$\FSharp.UIResources.dll")>]
 [<assembly: ProvideCodeBase(CodeBase = @"$PackageFolder$\Newtonsoft.Json.dll")>]

FSharp.Editor.fsproj

@@ -28,6 +28,11 @@
     <GeneratePkgDefFile>true</GeneratePkgDefFile>
     <IncludePkgdefInVSIXContainer>true</IncludePkgdefInVSIXContainer>
   </PropertyGroup>
+  <ItemGroup>
+    <InternalsVisibleTo Include="FSharp.ProjectSystem.FSharp" />
+    <InternalsVisibleTo Include="VisualFSharp.Unittests" />
+    <InternalsVisibleTo Include="VisualFSharp.Salsa" />
+  </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="FSharp.Editor.resx" GenerateSource="true">
       <GeneratedModuleName>Microsoft.VisualStudio.FSharp.Editor.SR</GeneratedModuleName>