[infer][java] model for Integer

Summary:
@public
This adds an Infer model for the Integer class in Java.

Test Plan: Manually inspected the specs, and added a test.

infer/models/java/src/java/lang/Integer.java

@@ -0,0 +1,28 @@
+package java.lang;
+
+public final class Integer {
+
+  public static int MAX_VALUE = 2147483647; // 2**31-1
+  public static int MIN_VALUE = -2147483648; // -2**31
+
+  protected final int value;
+
+  public Integer(int i) {
+    this.value = i;
+  }
+
+  public static Integer valueOf(int i) {
+    return new Integer(i);
+  }
+
+  public boolean equals(Object anObject) {
+    return anObject != null
+      && anObject instanceof Integer
+      && this.value == ((Integer) anObject).value;
+  }
+
+  public int intValue() {
+    return this.value;
+  }
+
+}

infer/tests/codetoanalyze/java/infer/IntegerExample.java

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+import java.util.HashMap;
+
+public class IntegerExample {
+
+    private static void testIntegerEquals() {
+        Integer a = new Integer(42);
+        Integer b = new Integer(42);
+        Integer c = null;
+
+        if (!a.equals(b)) {
+            c.intValue();
+        }
+
+        if (a != 42) {
+            c.intValue();
+        }
+    }
+
+}

infer/tests/endtoend/java/infer/IntegerClassTest.java

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+// Copyright (c) 2015-Present Facebook. All rights reserved.
+
+package endtoend.java.infer;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static utils.matchers.ResultContainsNoErrorInMethod.doesNotContain;
+
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import java.io.IOException;
+
+import utils.InferException;
+import utils.InferResults;
+
+public class IntegerClassTest {
+
+  public static final String SOURCE_FILE =
+      "infer/tests/codetoanalyze/java/infer/IntegerExample.java";
+
+  public static final String NULL_DEREFERENCE = "NULL_DEREFERENCE";
+
+  private static InferResults inferResults;
+
+  @BeforeClass
+  public static void loadResults() throws IOException {
+    inferResults = InferResults.loadInferResults(IntegerClassTest.class, SOURCE_FILE);
+  }
+
+  @Test
+  public void test()
+      throws InterruptedException, IOException, InferException {
+    assertThat(
+        "Results should not contain NPE errors",
+        inferResults,
+        doesNotContain(
+            NULL_DEREFERENCE,
+            SOURCE_FILE,
+            "testIntegerEquals"
+        )
+    );
+  }
+
+}