Extract Interface/Pull Up: Warn about private members with usages in the original class

#KT-15606 Fixed

idea/testData/refactoring/pullUp/k2k/privateMemberWithUsagesToClass.kt

@@ -0,0 +1,8 @@
+open class A
+
+class <caret>Foo : A() {
+    // INFO: {checked: "true"}
+    private fun privateFun() = 0
+
+    fun refer() = privateFun()
+}

idea/testData/refactoring/pullUp/k2k/privateMemberWithUsagesToClass.kt.after

@@ -0,0 +1,9 @@
+open class A {
+    // INFO: {checked: "true"}
+    protected fun privateFun() = 0
+}
+
+class Foo : A() {
+
+    fun refer() = privateFun()
+}

idea/testData/refactoring/pullUp/k2k/privateMemberWithUsagesToInterface.kt

@@ -0,0 +1,8 @@
+interface I
+
+class <caret>Foo : I {
+    // INFO: {checked: "true"}
+    private fun privateFun() = 0
+
+    fun refer() = privateFun()
+}

idea/testData/refactoring/pullUp/k2k/privateMemberWithUsagesToInterface.kt.messages

@@ -0,0 +1 @@
+Function 'fun privateFun(): Int' can't be moved to the interface because it's private and has usages in the original class