Refactored CS0077 Example with Modern C# Pattern Matching (#43108)

* Resolved issue 42861.

* Update docs/csharp/misc/cs0077.md

Thank you for the suggestion. Updating it.

Co-authored-by: Bartosz Klonowski <[email protected]>

* Update docs/csharp/misc/cs0077.md

Co-authored-by: Bartosz Klonowski <[email protected]>

* Update docs/csharp/misc/cs0077.md

Co-authored-by: Bartosz Klonowski <[email protected]>

* Update cs0077.md

* Update docs/csharp/misc/cs0077.md

---------

Co-authored-by: Adit Sheth <[email protected]>
Co-authored-by: Bartosz Klonowski <[email protected]>
Co-authored-by: Bill Wagner <[email protected]>

Author: 4 people

docs/csharp/misc/cs0077.md

@@ -13,6 +13,8 @@ ms.assetid: 55d3d290-d172-41a3-b326-ebf5a0a7e81f
 The as operator must be used with a reference type or nullable type ('int' is a non-nullable value type).  
 
  The [as](../language-reference/operators/type-testing-and-cast.md#as-operator) operator was passed a [value type](../language-reference/builtin-types/value-types.md). Because `as` can return [null](../language-reference/keywords/null.md), it can only be passed a [reference type](../language-reference/keywords/reference-types.md) or a [nullable value type](../language-reference/builtin-types/nullable-value-types.md).
+
+However, using [pattern matching](../fundamentals/functional/pattern-matching.md) with the [is](../language-reference/operators/is.md) operator, we can directly perform type checking and assignments in one step.
 
  The following sample generates CS0077:  
 
@@ -39,10 +41,13 @@ class M
       o1 = new C();  
       o2 = new S();  
 
-      s = o2 as S;  
-      // CS0077, S is not a reference type.  
-      // Try the following line instead.  
-      // c = o1 as C;  
+      s = o2 as S;    // CS0077, S is not a reference type
+
+      // Use pattern matching instead of as
+      if (o2 is S sValue)
+      {
+          s = sValue;
+      } 
    }  
 }  
 ```