Java: Add change note.

Author: aschackmull

java/ql/lib/change-notes/2026-02-18-cfg.md

@@ -0,0 +1,16 @@
+---
+category: breaking
+---
+* The Java control flow graph (CFG) implementation has been completely
+  rewritten. The CFG now includes additional nodes to more accurately represent
+  certain constructs. This also means that any existing code that implicitly
+  relies on very specific details about the CFG may need to be updated.
+  The CFG now only includes the nodes that are reachable from the entry point.
+  Additionally, the following breaking changes have been made:
+  - `ControlFlowNode.asCall` has been removed - use `Call.getControlFlowNode` instead.
+  - `ControlFlowNode.getEnclosingStmt` has been removed.
+  - `ControlFlow::ExprNode` has been removed.
+  - `ControlFlow::StmtNode` has been removed.
+  - `ControlFlow::Node` has been removed - this was merely an alias of
+    `ControlFlowNode`, which is still available.
+  - Previously deprecated predicates on `BasicBlock` have been removed.