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

idea/testData/refactoring/extractFunction/stringTemplates/fullEntryWithBlockExpr.kt

@@ -0,0 +1,8 @@
+// PARAM_DESCRIPTOR: value-parameter val a: kotlin.Int defined in foo
+// PARAM_TYPES: kotlin.Int
+fun foo(a: Int): String {
+    val x = "-${a + 1}"
+    val y = "x${a + 1}y"
+    val z = "x${a - 1}y"
+    return "abc<selection>${a + 1}</selection>def"
+}