Correct handling of local variables. We now correctly uniquify them
with regard to non-unique labels. Because local vars can effectively
have global scope we mostly want to treat them as global, but they're
uniquified relative to other globals very late in the process, so we
can't just throw them in the symbol table and be done. Fortunately
local variables exist in a separate namespace, so we just need to
uniquify the variables relative to the post-localization symbol table.
In other words, we take the symbol table, apply the label map, and
rename any variable that clashes.
This also fixes an older problem where we weren't masking the
leading '_' on variable labels when generating 64tass output.
The code list now makes non-unique labels obvious, but you can't tell
the difference between unique global and unique local. What's more,
the default type value in Edit Label is now adjusted to Global for
unique locals that were auto-generated. To make it a bit easier to
figure out what's what, the Info panel now has a "label type" line
that reports the type.
The 2023-non-unique-labels test had some additional tests added to
exercise conflicts with local variables. The 2019-local-variables
test output changed slightly because the de-duplicated variable
naming convention was simplified.
