Introduce Variable: Do not replace assignment left-hand sides

#KT-14240 Fixed

idea/testData/refactoring/introduceVariable/selectorAssignment.kt

@@ -0,0 +1,9 @@
+// WITH_RUNTIME
+class Foo(var bar: Bar)
+class Bar(var baz: Int)
+
+fun test() {
+    val foo = Foo(Bar(1))
+    println(<selection>foo.bar</selection>)
+    foo.bar.baz = foo.bar.baz + 1
+}