fix[lang]: fix certain varinfo comparisons

[charles-cooper]

What I did

fix #4163

How I did it

How to verify it

Commit message

for `VarInfo`s which are declared in memory, the `VarInfo`
initialization is missing `decl_node`, and therefore different
variables with the same type get detected as overlapping in loop
iterator modification detection. this commit properly initializes
memory `VarInfo`s with the appropriate `decl_node`.

Description for the changelog

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 44.72%. Comparing base (99304da) to head (562183a).

❗ There is a different number of reports uploaded between BASE (99304da) and HEAD (562183a). Click for more details.

HEAD has 139 uploads less than BASE

Flag	BASE (99304da)	HEAD (562183a)
	140	1

Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4164       +/-   ##
===========================================
- Coverage   91.36%   44.72%   -46.65%     
===========================================
  Files         109      109               
  Lines       15614    15616        +2     
  Branches     3436     3437        +1     
===========================================
- Hits        14266     6984     -7282     
- Misses        919     8028     +7109     
- Partials      429      604      +175     

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