JS frontend: allow to omit body for native functions and initializer for native properties. Additionally suppress UNUSED_PARAM for new nativeX annotations too.

compiler/testData/diagnostics/testsWithJsStdLib/native/unusedParam/nativeSetter.kt

@@ -0,0 +1,19 @@
+nativeSetter
+fun Int.foo(a: String, v: Int): Int = noImpl
+
+native
+class Bar(b: Int, c: Char) {
+    nativeSetter
+    fun baz(d: Int, v: Int) {}
+}
+
+native
+object Obj {
+    nativeSetter
+    fun test1(e: String, v: Any) {}
+
+    object Nested {
+        nativeSetter
+        fun test2(g: Int, v: Any) {}
+    }
+}