Right now, the strings are not used in comparisons, but they
are passed through the grammar processing pipeline, and are
available to the parse table construction algorithm.
This also cleans up a confusing aspect of the parse table
construction, in which precedences and associativities were
temporarily stored in the parse table data structure itself.
Previously, we attempted to completely separate the parse states
for item sets with non-terminal extras from the parse states
for other rules. But there was not a complete separation.
It actually isn't necessary to separate the parse states in this way.
The only special behavior for parse states with non-terminal extra rules
is what happens at the *end* of the rule: these parse states need to
perform an unconditional reduction.
Luckily, it's possible to distinguish these *non-terminal extra ending*
states from other states just based on their normal structure, with
no additional state.
