Introduce Parameter: Support extraction of string template fragments

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

@@ -0,0 +1,6 @@
+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"
+}