Update SA1119 for stackalloc expressions

Author: nxtn

StyleCop.Analyzers/StyleCop.Analyzers.Test.CSharp8/MaintainabilityRules/SA1119CSharp8UnitTests.cs

@@ -152,5 +152,21 @@ public unsafe string TestMethod(int n, byte* a, byte* b)
 
             await VerifyCSharpDiagnosticAsync(LanguageVersion.CSharp8, testCode, DiagnosticResult.EmptyDiagnosticResults, CancellationToken.None).ConfigureAwait(false);
         }
+
+        [Fact]
+        public async Task TestStackAllocExpressionInExpressionAsync()
+        {
+            const string testCode = @"public class TestClass
+{
+    public unsafe void TestMethod()
+    {
+        var ptr = stackalloc byte[1];
+        var span = (stackalloc byte[1]);
+    }
+}
+";
+
+            await VerifyCSharpDiagnosticAsync(LanguageVersion.CSharp8, testCode, DiagnosticResult.EmptyDiagnosticResults).ConfigureAwait(false);
+        }
     }
 }

StyleCop.Analyzers/StyleCop.Analyzers.Test/Verifiers/StyleCopCodeFixVerifier`2.cs

@@ -45,7 +45,7 @@ internal static Task VerifyCSharpDiagnosticAsync(string source, DiagnosticResult
         internal static Task VerifyCSharpDiagnosticAsync(LanguageVersion? languageVersion, string source, DiagnosticResult expected, CancellationToken cancellationToken)
             => StyleCopDiagnosticVerifier<TAnalyzer>.VerifyCSharpDiagnosticAsync(languageVersion, source, expected, cancellationToken);
 
-        internal static Task VerifyCSharpDiagnosticAsync(LanguageVersion? languageVersion, string source, DiagnosticResult[] expected, CancellationToken cancellationToken)
+        internal static Task VerifyCSharpDiagnosticAsync(LanguageVersion? languageVersion, string source, DiagnosticResult[] expected, CancellationToken cancellationToken = default)
             => StyleCopDiagnosticVerifier<TAnalyzer>.VerifyCSharpDiagnosticAsync(languageVersion, source, settings: null, expected, cancellationToken);
 
         internal static Task VerifyCSharpDiagnosticAsync(LanguageVersion? languageVersion, string source, string settings, DiagnosticResult[] expected, CancellationToken cancellationToken)

StyleCop.Analyzers/StyleCop.Analyzers/MaintainabilityRules/SA1119StatementMustNotUseUnnecessaryParenthesis.cs

@@ -137,6 +137,12 @@ private static void HandleParenthesizedExpression(SyntaxNodeAnalysisContext cont
                         return;
                     }
 
+                    if (node.Expression.IsKind(SyntaxKind.StackAllocArrayCreationExpression)
+                        && node.Parent.IsKind(SyntaxKind.EqualsValueClause))
+                    {
+                        return;
+                    }
+
                     ReportDiagnostic(context, node);
                 }
                 else