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/nativeGetter.kt

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