Introduce Parameter: Support extraction of string template fragments

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

@@ -0,0 +1,7 @@
+fun foo(param: Int): String {
+    val x = "a1234_"
+    val y = "-4123a"
+    val z = "+1243a"
+    val u = 123
+    return "ab<selection>123</selection>def"
+}