Major Description
This effort started with the patch on LUCENE-4556, to create a "light
weight" replacement for the current object-heavy Automaton class
(which creates separate State and Transition objects).
I took that initial patch much further, and cutover most places in
Lucene that use Automaton to LightAutomaton. Tests pass.
The core idea of LightAutomaton is all states are ints, and you build
up the automaton under the restriction that you add all outgoing
transitions one state at a time. This worked well for most
operations, but for some (e.g. UTF32ToUTF8!!) it was harder, so I also
added a separate builder to add transitions in any order and then in
the end they are sorted and added to the real automaton.
If this is successful I think we should just replace the current
Automaton with LightAutomaton; right now they both exist in my current
patch...
This is very much a work in progress, and I'm not sure the
restrictions the API imposes are "reasonable" (some algos got uglier).
But I think it's at least worth exploring/iterating... I'll make a branch and
commit my current state.