Uses solution file to do dotnet pack

Now that we have Directory.Build.props, it can set everything in the src directory to IsPackable and everything else can be set to not IsPackable.  This allows a condierable speed boost when doing dotnet pack since we don't have to hit the overhead of MSBuild for each package.

Author: TheAngryByrd

build.fsx

@@ -138,9 +138,7 @@ Target.create "AssemblyInfo" (fun _ ->
 
 let releaseNotes = String.toLines release.Notes
 Target.create "NuGet" (fun _ ->
-    ["src/FsToolkit.ErrorHandling"
-     "src/FsToolkit.ErrorHandling.TaskResult"
-     "src/FsToolkit.ErrorHandling.JobResult"]
+    [solutionFile]
     |> Seq.iter (
       DotNet.pack(fun p ->
            { p with