java: rewrite conflict detection

- favour unary predicates over binary ones
(the natural "conflicting access" is binary)
- switch to a dual solution to trade recursion through forall for simple existentials.

Co-authored-by: Anders Schack-Mulligen <aschackmull@github.com>

java/ql/test/query-tests/ThreadSafe/examples/Test.java

@@ -40,7 +40,7 @@ public class Test {
    */
   public void setYCorrect(int y) {
     lock.lock();
-    this.y = y; // $ Alert
+    this.y = y;
     lock.unlock();
   }
 
@@ -49,7 +49,7 @@ public class Test {
    * @param y
    */
   private void setYPrivate(int y) {
-    this.y = y;
+    this.y = y; // $ Alert
   }
 
   /**
@@ -57,7 +57,7 @@ public class Test {
    * @param y
    */
   public void setYWrongLock(int y) {
-    this.y = y;
+    this.y = y; // $ Alert
     lock.lock();
     lock.unlock();
   }
@@ -71,6 +71,6 @@ public class Test {
   }
 
   public void testMethod() {
-    this.y = y + 2;
+    this.y = y + 2; // $ Alert
   }
 }