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/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);
+}