Make annotations-modifiers private and fix some lost usages

It's needed to prevent usages of them as real annotation/type.
But we can't remove them, because currently some modifiers
are artificially resolved as annotations of those classes.

compiler/testData/codegen/boxWithStdlib/fullJdk/native/nativePropertyAccessors.kt

@@ -1,27 +1,27 @@
 class C {
     companion object {
         val defaultGetter: Int = 1
-            @external get
+            external get
 
         var defaultSetter: Int = 1
-            @external get
-            @external set
+            external get
+            external set
     }
 
     val defaultGetter: Int = 1
-        @external get
+        external get
 
     var defaultSetter: Int = 1
-        @external get
-        @external set
+        external get
+        external set
 }
 
 val defaultGetter: Int = 1
-    @external get
+    external get
 
 var defaultSetter: Int = 1
-    @external get
-    @external set
+    external get
+    external set
 
 fun check(body: () -> Unit, signature: String): String? {
     try {