Fix aspnet/AspNetCoredotnet/aspnetcore-tooling#6187

The bug here is that we have extra whitespace being written out when the
component renders. This happens because parser adds an empty C#
statement node to wrap all of the whitespace that precedes `@functions`.
This is tracked by aspnet/AspNetCoredotnet/aspnetcore-tooling#6207.

To fix this issue I'm allowing the whitespace pass to skip over an empty
C# statement to remove whitespace. This is sound because an empty C#
statement produces no output - we allow removing whitespace before and
after all nodes that produce no output.
\n\nCommit migrated from e68d93f458

src/Razor/Microsoft.AspNetCore.Razor.Language/src/Components/ComponentWhitespacePass.cs

@@ -77,8 +77,11 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
                         break;
 
                     case CSharpCodeIntermediateNode codeIntermediateNode:
+                        // A C# code node could be empty. We can't remove them, but we can skip them. 
                         shouldRemoveNode = false;
-                        shouldContinueIteration = ComponentDocumentClassifierPass.IsBuildRenderTreeBaseCall(codeIntermediateNode);
+                        shouldContinueIteration = 
+                            IsEmpty(codeIntermediateNode) || 
+                            ComponentDocumentClassifierPass.IsBuildRenderTreeBaseCall(codeIntermediateNode);
                         break;
 
                     default:
@@ -110,5 +113,18 @@ namespace Microsoft.AspNetCore.Razor.Language.Components
             Forwards,
             Backwards
         }
+
+        private static bool IsEmpty(CSharpCodeIntermediateNode node)
+        {
+            for (var i = 0; i < node.Children.Count; i++)
+            {
+                if (!(node.Children[i] is IntermediateToken token && string.IsNullOrWhiteSpace(token.Content)))
+                {
+                    return false;
+                }
+            }
+
+            return true;
+        }
     }
 }