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/noDelimiterWithOverload.kt

@@ -0,0 +1,11 @@
+// "Insert lacking comma(s) / semicolon(s)" "true"
+
+enum class MyEnum {
+    A {
+        override fun foo(): Int = 13
+    }
+    B C<caret> {
+        override fun foo(): Int = 23
+    }
+    open fun foo(): Int = 42
+}