unused return value: report native methods (IDEA-90127)

java/java-tests/testData/inspection/unusedReturnValue/native/expected.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<problems>
+  <problem>
+    <file>Test.java</file>
+    <line>2</line>
+    <description>Return value of the method is never used</description>
+  </problem>
+</problems>

java/java-tests/testData/inspection/unusedReturnValue/native/src/Test.java

@@ -0,0 +1,7 @@
+class Test {
+  private static native boolean isUnused();
+
+  public static void main(String[] args) {
+    Test.isUnused();
+  }
+}