CPP: Add changenote for adding delete to the IR.

Author: alexet

cpp/ql/lib/change-notes/2023-08-29-delete-ir.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* `delete` and `delete[]` are now modeled as calls to the relevant `operator delete` in the IR. In the case of a dynamic delete call a new instruction `VirtualDeleteFunctionAddress` is used to represent a function that dispatches to the correct delete implementation.