Unlike 64tass and Merlin, which allow you to redefine symbols, ACME
uses "zones" that provide scope for local variables. This means
that, at the point of a local variable table definition, we have to
start a new zone and output the full set of active symbols, not just
the newly-defined ones. (If you set the "clear previous" flag in
the LvTable there's no difference.)
We could do a bit better by only outputting the symbols that are
actually used within the zone, similar to what we do for global
project/platform symbols, but that's a bunch of work for questionable
benefit.
After thrashing around a bit, I had to choose between making the
uniquifier more complicated, or making de-duplication a separate
step. Since I don't really expect duplicates to be a thing, I went
with the latter.
Updated the regression test.
This hits most of the edge cases, but doesn't exercise the two
duplicate name situations (var name same as user label, var name
same as project/platform symbol).
Also, fixed a bug in the EditDefSymbol uniqueness check where it
was comparing a symbol to itself.
Variables are now handled properly end-to-end, except for label
uniquification. So cc65 and ACME can't yet handle a file that
redefines a local variable.
This required a bunch of plumbing, but I think it came out okay.
