Incremental Generators documentation fixes (#67593)

* Simplify example (use local variable).

* Remove incorrect indentation.

* Use correct SymbolKind field name.

Author: davecluderay

docs/features/incremental-generators.md

@@ -658,7 +658,7 @@ inputs and combine them into a single source of data. For example:
 IncrementalValuesProvider<AdditionalText> additionalTexts = initContext.AdditionalTextsProvider;
 
 // combine each additional text with the parse options
-IncrementalValuesProvider<(AdditionalText, ParseOptions)> combined = initContext.AdditionalTextsProvider.Combine(initContext.ParseOptionsProvider);
+IncrementalValuesProvider<(AdditionalText, ParseOptions)> combined = additionalTexts.Combine(initContext.ParseOptionsProvider);
 
 // perform a transform on each text, with access to the options
 var transformed = combined.Select(static (pair, _) => 
@@ -731,7 +731,7 @@ As an author I can make an input node that extracts the return type information
 
 ```csharp
 // create a syntax provider that extracts the return type kind of method symbols
-    var returnKinds = initContext.SyntaxProvider.CreateSyntaxProvider(static (n, _) => n is MethodDeclarationSyntax,
+var returnKinds = initContext.SyntaxProvider.CreateSyntaxProvider(static (n, _) => n is MethodDeclarationSyntax,
                                                                   static (n, _) => ((IMethodSymbol)n.SemanticModel.GetDeclaredSymbol(n.Node)).ReturnType.Kind);
 ```
 
@@ -768,7 +768,7 @@ public class Class4
 The `predicate` will be re-run for `file1.cs` as it has changed, and will pick
 out the method symbol `Method1()` again.  Next, because the `transform` is
 re-run for _all_ the methods, the return type kind for `Method2()` is correctly
-changed to `Error` as `Class1` no longer exists.
+changed to `ErrorType` as `Class1` no longer exists.
 
 Note that we didn't need to run the `predicate` over for nodes in `file2.cs`
 even though they referenced something in `file1.cs`. Because the first check is