Introduce Parameter: Support extraction of string template fragments

idea/testData/refactoring/introduceParameter/stringTemplates/fullContent.kt

@@ -0,0 +1,6 @@
+fun foo(a: Int): String {
+    val x = "abc$a"
+    val y = "abc${a}"
+    val z = "abc{$a}def"
+    return "<selection>abc$a</selection>" + "def"
+}