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

idea/testData/refactoring/extractFunction/stringTemplates/fullContent.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 = s(a)
+    val y = s(a)
+    val z = "abc{$a}def"
+    return s(a) + "def"
+}
+
+private fun s(a: Int) = "abc$a"