Convert parameter to receiver: don't remove 'override' and 'vararg' when function has 'vararg' parameter

#KT-28851 Fixed

idea/testData/intentions/convertParameterToReceiver/hasVararg.kt

@@ -0,0 +1,7 @@
+interface A {
+    fun foo(<caret>s: String, vararg args: Any)
+}
+class B : A {
+    override fun foo(s: String, vararg args: Any) {
+    }
+}

idea/testData/intentions/convertParameterToReceiver/hasVararg.kt.after

@@ -0,0 +1,7 @@
+interface A {
+    fun String.foo(vararg args: Any)
+}
+class B : A {
+    override fun String.foo(vararg args: Any) {
+    }
+}