fix: assignment when rhs is complex type and references lhs

[charles-cooper]

What I did

fix #2418

How I did it

check that rhs and lhs do not overlap in parse_Assign. if they do, copy rhs to a temporary buffer, then copy to the lhs. this might not be the most efficient approach, but it is safe (and it's a relatively rare case to see in user code).

note that this doesn't touch make_setter directly because it would need access to the memory allocator (to allocate the temporary buffer). this would result in the fix not working in other cases where the arguments to make_setter overlap. i don't think there are any cases of those, but if there were, they would need to be fixed on a case by case basis.

How to verify it

test cases fail on master (97ff017) but pass on this branch.

Commit message

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Description for the changelog

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[codecov-commenter]

Codecov Report

Merging #3410 (71b36df) into master (97ff017) will decrease coverage by 0.07%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##           master    #3410      +/-   ##
==========================================
- Coverage   88.96%   88.89%   -0.07%     
==========================================
  Files          86       86              
  Lines       10765    10788      +23     
  Branches     2445     2448       +3     
==========================================
+ Hits         9577     9590      +13     
- Misses        786      796      +10     
  Partials      402      402              

Impacted Files	Coverage Δ
vyper/codegen/context.py	91.91% <100.00%> (+0.12%)	⬆️
vyper/codegen/expr.py	87.67% <100.00%> (+0.17%)	⬆️
vyper/codegen/ir_node.py	91.24% <100.00%> (+0.21%)	⬆️
vyper/codegen/stmt.py	89.76% <100.00%> (+0.29%)	⬆️
vyper/semantics/analysis/base.py	81.50% <100.00%> (+0.25%)	⬆️

... and 5 files with indirect coverage changes

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