Prohibit assigning single elements into varargs in named form

#KT-20588 Fixed
 #KT-20589 Fixed

compiler/testData/diagnostics/tests/varargs/prohibitAssigningSingleElementsInNamedForm.kt

@@ -0,0 +1,20 @@
+// !LANGUAGE: +ProhibitAssigningSingleElementsToVarargsInNamedForm
+// !DIAGNOSTICS: -UNUSED_PARAMETER
+
+annotation class Anno1(vararg val s: String)
+annotation class Anno2(vararg val i: Int)
+
+@Anno1(s = <!ASSIGNING_SINGLE_ELEMENT_TO_VARARG_IN_NAMED_FORM_ANNOTATION_ERROR!>"foo"<!>)
+@Anno2(i = *<!ASSIGNING_SINGLE_ELEMENT_TO_VARARG_IN_NAMED_FORM_ANNOTATION!>intArrayOf(1)<!>)
+fun f1() {}
+
+@Anno1(s = ["foo"])
+@Anno2(i = intArrayOf(1))
+fun f2() {}
+
+fun foo(vararg ints: Int) {}
+
+fun test() {
+    foo(ints = <!ASSIGNING_SINGLE_ELEMENT_TO_VARARG_IN_NAMED_FORM_FUNCTION_ERROR!>1<!>)
+    foo(ints = *intArrayOf(1))
+}