Quick fix for enum entry delimiter syntax fix, together with a set of tests.

Possible NPE in getNextSiblingIgnoringWhitespace fixed. Some warnings also removed.
Last comma is replaced by semicolon. Comments are taken into account.

idea/testData/quickfix/migration/enumDelimiter/noCommaComment.kt

@@ -0,0 +1,8 @@
+// "Insert lacking comma(s) / semicolon(s)" "true"
+
+enum class MyEnum {
+    FIRST<caret>
+    /* The first one */ 
+    SECOND 
+    /* The last one */
+}