Fix NumericTokenizer.

NumericTokenizer is a simple wrapper aroung a NumericTokenStream. However, its
implementations had a few issues: its reset() method was not idempotent,
causing exceptions if reset() was called twice (causing #3211) and it had no
attributes, meaning that the only thing it allowed to do is counting the number
of generated tokens. The reason why indexing numeric data worked is that
the mapper's parseCreateField directly generates a NumericTokenStream and
by-passes the analyzer.

This commit makes NumericTokenizer.reset idempotent and makes consuming a
NumericTokenizer behave the same way as consuming the underlying
NumericTokenStream.