Minor improvement in convert to string template inspection: no highlighting when the expression is split onto multiple lines

idea/testData/intentions/convertToStringTemplate/onMultipleLines.kt

@@ -0,0 +1,5 @@
+fun foo(p: Int) {
+    val v = <caret>"line 1\n" +
+            "line 2: " + p + "\n" +
+            "line 3"
+}

idea/testData/intentions/convertToStringTemplate/onMultipleLines.kt.after

@@ -0,0 +1,3 @@
+fun foo(p: Int) {
+    val v = "line 1\nline 2: $p\nline 3"
+}