C#: Add ExperimentalAttribute class.

Author: michaelnebel

csharp/ql/lib/semmle/code/csharp/frameworks/system/diagnostics/CodeAnalysis.qll

@@ -0,0 +1,15 @@
+/** Provides definitions related to the namespace `System.Diagnostics.CodeAnalysis`. */
+
+private import csharp
+
+/** An attribute of type `System.Diagnostics.CodeAnalysis.ExperimentalAttribute`. */
+class ExperimentalAttribute extends Attribute {
+  ExperimentalAttribute() {
+    this.getType().hasFullyQualifiedName("System.Diagnostics.CodeAnalysis", "ExperimentalAttribute")
+  }
+
+  /**
+   * Gets the diagnostic ID.
+   */
+  string getId() { result = this.getConstructorArgument(0).getValue() }
+}