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

idea/testData/refactoring/introduceProperty/stringTemplates/fullContent.kt.after

@@ -0,0 +1,11 @@
+// EXTRACTION_TARGET: property with initializer
+val a = 1
+
+private val s = "abc$a"
+
+fun foo(): String {
+    val x = s
+    val y = s
+    val z = "abc{$a}def"
+    return s + "def"
+}