Report warning on modifier list of primary ctor unless 'constructor' keyword specified

compiler/testData/diagnostics/tests/modifiers/primaryConstructorMissingKeyword.kt

@@ -0,0 +1,9 @@
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+annotation class Ann(val x: Int = 1)
+class A <!MISSING_CONSTRUCTOR_KEYWORD!>private<!> (val x: Int) {
+inner class B <!MISSING_CONSTRUCTOR_KEYWORD!>Ann(2)<!> (val y: Int)
+
+fun foo() {
+    class C <!MISSING_CONSTRUCTOR_KEYWORD!>private @Ann(3)<!> (args: Int)
+    }
+}