Extract Function: Allow to select fragments which start with comment

idea/testData/refactoring/extractFunction/basic/fragmentWithComment.kt

@@ -0,0 +1,7 @@
+// NEXT_SIBLING:
+fun foo(a: Int): Int {
+    <selection>// test
+    println(a)
+    if (a > 0) return a</selection>
+    return -a
+}