C#: Add change note for #3110

Author: hvitved

change-notes/1.25/analysis-csharp.md

@@ -24,5 +24,28 @@ The following changes in version 1.25 affect C# analysis in all applications.
   have type parameters. This means that non-generic nested types inside construced types,
   such as `A<int>.B`, no longer are considered unbound generics. (Such nested types do,
   however, still have relevant `.getSourceDeclaration()`s, for example `A<>.B`.)
+* The data-flow library has been improved, which affects and improves most security queries. Flow
+  through methods now takes nested field reads/writes into account. For example, the library is
+  able to track flow from `"taint"` to `Sink()` via the method `GetF2F1()` in
+  ```csharp
+  class C1
+  {
+      string F1;
+  }
+
+  class C2
+  {
+      C1 F2;
+  
+
+      string GetF2F1() => this.F2.F1; // Nested field read
+
+      void M()
+      {
+          this.F2 = new C1() { F1 = "taint" };
+          Sink(this.GetF2F1()); // NEW: "taint" reaches here
+      }
+  }
+  ```
 
 ## Changes to autobuilder