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

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

@@ -0,0 +1,9 @@
+private val b = true
+
+// EXTRACTION_TARGET: property with initializer
+fun foo(): String {
+    val x = "a${b}123"
+    val x = "aTRUE123"
+    val z = true
+    return "ab${b}def"
+}