* Concurrency fixes and refactoring for clarity

Removed builder reference from SymbolicRegexNode instances; builder now
has to be passed in. Since the builder is not thread safe this clarifies
the locking required in the matcher when using it.
Moved matching specific state from the builder to the matcher. This
includes state and transition arrays.
Simplify character kind code by eliminating duplication of logic.

* Changes from review and cleanup

DfaMatchingState is now just MatchingState

* Comment on NFA mode IDs