Add patterns module: pattern matching from JDK 21 to 27

Type, record and primitive patterns, guards, sealed exhaustiveness, MatchException via separate compilation, and eight captured transcripts.

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01TF9JWFvJSNm6HVzswzZU5a

patterns/sep/client/Client.java

@@ -0,0 +1,14 @@
+public class Client {
+    // Compiled against Shape v1, where the only permitted subtypes are Circle and Square.
+    public static double area(Shape s) {
+        return switch (s) {
+            case Circle c -> Math.PI * c.r() * c.r();
+            case Square q -> q.side() * q.side();
+        };
+    }
+
+    public static void main(String[] args) {
+        System.out.println("circle: " + area(new Circle(1)));
+        System.out.println("square: " + area(new Square(2)));
+    }
+}

patterns/sep/v1/Circle.java

@@ -0,0 +1 @@
+public record Circle(double r) implements Shape {}

patterns/sep/v1/Shape.java

@@ -0,0 +1 @@
+public sealed interface Shape permits Circle, Square {}

patterns/sep/v1/Square.java

@@ -0,0 +1 @@
+public record Square(double side) implements Shape {}

patterns/sep/v2/Circle.java

@@ -0,0 +1 @@
+public record Circle(double r) implements Shape {}

patterns/sep/v2/Main.java

@@ -0,0 +1,6 @@
+public class Main {
+    public static void main(String[] args) {
+        // Triangle exists only in v2. Client was compiled before it did.
+        System.out.println("triangle: " + Client.area(new Triangle(3, 4)));
+    }
+}

patterns/sep/v2/Shape.java

@@ -0,0 +1 @@
+public sealed interface Shape permits Circle, Square, Triangle {}

patterns/sep/v2/Square.java

@@ -0,0 +1 @@
+public record Square(double side) implements Shape {}

patterns/sep/v2/Triangle.java

@@ -0,0 +1 @@
+public record Triangle(double base, double height) implements Shape {}