Bind contexts (a.k.a. tags) to DFA transitions, not states.

Bind contexts (a.k.a. tags) to DFA transitions, not states.

This is a very imortant change: it makes tracing tag conflicts as
simple as comparing tags on transitions during DFA construction.
If during determinization we get two identical transitions that
differ only in tags, then we have a tag conflict. Tags that cause
conflicts are called non-deterministic (since they don't allow
deterministic match).

This approach if very similar to Ville Laurikari's TDFA: as he does,
we first build TNFA and then apply determinization; however Laurikari's
TDFA uses complex bookkeeping to track all possible tag values,
while re2c simply forbids tags that cannot be matche efficiently.

Binding tags to transitions allows more fine-grained liveness
analyses, dead tag elimination and tag deduplication.