Forbid usage of Character.codePoint(At|Before) and Collections.sort.

Character.codePointAt and codePointBefore have two versions: one which only
accepts an offset, and one which accepts an offset and a limit. The former can
be dangerous when working with buffers of characters because if the offset
is the last char of the buffer, a char outside the buffer might be used to
compute the code point, so one should always use the version which accepts a
limit.

Collections.sort is wasteful on random-access lists: it dumps data into an
array, sorts the list and then adds elements back to the list. However, the
sorting can easily be performed in-place by using Lucene's
CollectionUtil.(merge|quick|tim)Sort.