Add NumberOfNavigateToCodeView metric

Add metric for navigating from editable diff (e.g. `View Changes in
Solution`) to code view.

Author: jcansdale

src/GitHub.Exports/Models/UsageModel.cs

@@ -76,6 +76,7 @@ public class MeasuresModel
             public int NumberOfUpstreamsAddedWhenForkingRepo { get; set; }
             public int NumberOfTrackMasterUpstreamWhenForkingRepo { get; set; }
             public int NumberOfNavigateToPullRequestFileDiff { get; set; }
+            public int NumberOfNavigateToCodeView { get; set; }
             public int ExecuteToggleInlineCommentMarginCommand { get; set; }
             public int NumberOfPullRequestFileMarginToggleInlineCommentMargin { get; set; }
             public int NumberOfPullRequestFileMarginViewChanges { get; set; }

src/GitHub.VisualStudio/Commands/GoToSolutionOrPullRequestFileCommand.cs

@@ -68,6 +68,9 @@ public override async Task Execute()
                 bool isEditableDiff = pullRequestEditorService.Value.IsEditableDiff(textView);
                 if (isEditableDiff)
                 {
+                    // Navigating from editable diff to code view
+                    await usageTracker.Value.IncrementCounter(x => x.NumberOfNavigateToCodeView);
+
                     // Open active document in Code View
                     pullRequestEditorService.Value.OpenActiveDocumentInCodeView(sourceView);
                     return;