introduce quickfix for change visiblity from private to internal for private top-level declarations

idea/testData/quickfix/privateInFiles/privateTopLevelVarWithSetterInFile.before.Main.kt

@@ -0,0 +1,7 @@
+// "Make <set-prop> internal" "true"
+
+package test
+
+fun foo() {
+    <caret>prop = 20
+}