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

idea/testData/refactoring/introduceProperty/stringTemplates/rawTemplateWithSubstring.kt

@@ -0,0 +1,12 @@
+// EXTRACTION_TARGET: property with initializer
+val a = 1
+
+fun foo(): String {
+    val x = """_c$a
+    :${a + 1}d_"""
+    val y = "_$a:${a + 1}d_"
+    val z = """_c$a:${a + 1}d_"""
+    val u = "_c$a\n:${a + 1}d_"
+    return """ab<selection>c$a
+    :${a + 1}d</selection>ef"""
+}