Adding Update, Exclude, and Remove everywhere they currently are not.

This fixes dotnet#68, at least the ArgumentNullException part -- targets files without an Sdk attribute don't seem to work.

Author: cdonnellytx

src/ProjectFileTools/Completion/PackageCompletionSource.cs

@@ -22,6 +22,9 @@ internal class PackageCompletionSource : ICompletionSource
         private static readonly IReadOnlyDictionary<string, string> AttributeToCompletionTypeMap = new Dictionary<string, string>(StringComparer.Ordinal)
         {
             {"Include", "Name" },
+            {"Update", "Name" },
+            {"Exclude", "Name" },
+            {"Remove", "Name" },
             {"Version", "Version" }
         };
 
@@ -85,7 +88,10 @@ public static bool TryGetPackageInfoFromXml(XmlInfo info, out string packageName
                 && info.AttributeName != null && AttributeToCompletionTypeMap.ContainsKey(info.AttributeName)
                 && info.TryGetElement(out XElement element))
             {
-                XAttribute name = element.Attribute(XName.Get("Include"));
+                XAttribute name = element.Attribute(XName.Get("Include"))
+                    ?? element.Attribute(XName.Get("Update"))
+                    ?? element.Attribute(XName.Get("Exclude"))
+                    ?? element.Attribute(XName.Get("Remove"));
                 XAttribute version = element.Attribute(XName.Get("Version"));
                 packageName = name?.Value;
                 packageVersion = version?.Value;

src/ProjectFileTools/GoToDefinition/GoToDefinitionController.cs

@@ -145,7 +145,7 @@ internal static GotoDefinitionController CreateAndRegister(IWpfTextView textview
         {
             ThreadHelper.ThrowIfNotOnUIThread();
 
-            if (info.AttributeName == "Include")
+            if (info.AttributeName == "Include" || info.AttributeName == "Update" || info.AttributeName == "Exclude" || info.AttributeName == "Remove")
             {
                 string relativePath = info.AttributeValue;
                 IWorkspace workspace = workspaceManager.GetWorkspace(textDoc.FilePath);