During prefilter region replacement, turn regions with very large max
bounds into repeats with inf max bound. This improves compile time and
the likelihood that we will actually be able to build an implementation
for such patterns.
This allows sibling character classes to be merged together before graph
component splitting is done by calcComponents().
In particular, this transforms (A|a)(B|b)(C|c) into [Aa][Bb][Cc]
earlier.
As somMayGoBackwards() operates on a copy of the graph where virtual
starts have been collapsed on to startDs, we need to be careful not to
create parallel edges.
This changes all the execute_graph() interfaces so that instead of
mutating a std::set of vertices, they accept an initial flat_set of
states and return a resultant flat_set of states after execution.
(Note that internally execute_graph() still uses bitsets)
This is both faster and more flexible.
