Extract Function/Introduce Property: Support extraction of string template fragments

idea/testData/refactoring/extractFunction/stringTemplates/fullEntryWithSimpleName.kt.after

@@ -0,0 +1,10 @@
+// PARAM_DESCRIPTOR: value-parameter val a: kotlin.Int defined in foo
+// PARAM_TYPES: kotlin.Int, Number, Comparable<Int>, java.io.Serializable, Any
+fun foo(a: Int): String {
+    val x = "-$a"
+    val y = "x${a}y"
+    val z = "x$ay"
+    return "abc${i(a)}def"
+}
+
+private fun i(a: Int) = a