extract method: check duplicates/used vars also in unreachable code

(cherry picked from commit 42249fe8f0cead1a0023aa9edfb23fc52a95c268)

java/java-tests/testData/refactoring/extractMethod/DuplicateInUnreachableCode.java

@@ -0,0 +1,16 @@
+
+class A {
+  private static final boolean ourOverrideFinalFields = false;
+
+  public static String createShared(char[] chars) {
+
+    if (ourOverrideFinalFields) {
+      String s = new String();
+      return s;
+    }
+    String s = <selection>new String()</selection>;
+    return new String(chars);
+  }
+
+
+}

java/java-tests/testData/refactoring/extractMethod/DuplicateInUnreachableCode_after.java

@@ -0,0 +1,22 @@
+import org.jetbrains.annotations.NotNull;
+
+class A {
+  private static final boolean ourOverrideFinalFields = false;
+
+  public static String createShared(char[] chars) {
+
+    if (ourOverrideFinalFields) {
+      String s = newMethod();
+      return s;
+    }
+    String s = newMethod();
+    return new String(chars);
+  }
+
+    @NotNull
+    private static String newMethod() {
+        return new String();
+    }
+
+
+}