Rewrite most gensym macros to use automatic hygiene instead (#59239)
Manual `gensym` code often contains a lot of mistakes, either because the
user uses something like `.` or `+`, or because it combines code from
multiple modules (gensym is only unique within a pre-compile unit). This
replaces most uses for macro local variables with proper scope markers.
I did not rewrite `_lift_one_interp_helper` or `replace_ref_begin_end_`
however, since, while possible by adding `esc` to every argument that
has not used a gensym value, if any other argument did is a value, I
worried that could lead to macroexpand.scm making more new mistakes so I
left if for a separate PR. Better yet, we could make a unhygienic-scope
and unescape pair for marking the inverse/dual of the usual operations
(marking a symbol as unescaped within a region of unhygienic (escaped)
code to make these various uses easier to implement.
But also do rewrite `replace_ref_begin_end_` to respect argument order
and evaluation count (similar to its julia-syntax.scm counterpart) and
scoping (not adding `let` unpredictably).
julia
8190fe87 - Rewrite most gensym macros to use automatic hygiene instead (#59239)
