Java slicing: support -> this/-> paramN contracts

Fixes IDEA-121571 Feature request: A Contract Annotation that indicates that a method returns its argument

java/java-tests/testData/codeInsight/slice/backward/Append.java

@@ -0,0 +1,6 @@
+class Test {
+  StringBuilder builder(StringBuilder <flown1111>sb) {
+    StringBuilder foo = <flown111><flown11><flown1>sb.append("foo").append(123);
+    return <caret>foo;
+  }
+}

java/java-tests/testData/codeInsight/slice/backward/InterMethod.java

@@ -10,11 +10,11 @@ class WW {
     }
 
     {
-        x(<flown111111>"zzz");
+        x(<flown1211><flown111111>"zzz");
     }
 
-    String x(String <flown11111>g) {
-        String d = <flown1>foo(<flown1111>g);
+    String x(String <flown121><flown11111>g) {
+        String d = <flown1>foo(<flown12><flown1111>g);
         return <caret>d;
     }
 

java/java-tests/testData/codeInsight/slice/backward/RequireNonNull.java

@@ -0,0 +1,21 @@
+class Test {
+
+  private String <flown1>s;
+  private String s2;
+
+  void test(String <flown112111><flown1111>s, String s2) {
+    this.s = <flown11>requireNonNull(<flown11211><flown111>s);
+    this.s2 = requireNonNull(s2);
+  }
+
+  String foo() {
+    return <caret>s;
+  }
+
+  public static <T> T requireNonNull(T <flown1121>obj) {
+    if (obj == null)
+      throw new NullPointerException();
+    return <flown112>obj;
+  }
+
+}

java/java-tests/testData/codeInsight/slice/forward/Append.java

@@ -0,0 +1,6 @@
+class Test {
+  StringBuilder <flown111111>builder(StringBuilder <caret>sb) {
+    StringBuilder <flown1111>foo = <flown111><flown11><flown1>sb.append("foo").append(1);
+    return <flown11111>foo;
+  }
+}

java/java-tests/testData/codeInsight/slice/forward/RequireNonNull.java

@@ -0,0 +1,16 @@
+class Test {
+  private String <flown111>s;
+  private String s2;
+
+  void test(String <caret>s, String s2) {
+    this.s = <flown11>requireNonNull(<flown1>s);
+    this.s2 = requireNonNull(s2);
+  }
+
+  String <flown11111>foo() {
+    return <flown1111>s;
+  }
+
+  @org.jetbrains.annotations.Contract("null -> fail; !null -> param1")
+  public static native <T> T requireNonNull(T <flown12>obj);
+}