allow variable access on constant/literal arrays

[charles-cooper]

What I did

Fix #2156 and #2130

Note that a bug similar to #2130 can still be triggered with a list of ambiguous type. For instance, MY_LIST: constant(uint256[1]) = [1]. I used a decimal in the test to demonstrate that the array literals pass but the type checker issue still needs to be addressed.

How I did it

Expand the logic in Expr.parse_Subscript to handle constants/literals

How to verify it

See test

Description for the changelog

Allow variable access on constant/literal arrays

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[codecov-commenter]

Codecov Report

Merging #2534 (d101640) into master (9a5dd50) will increase coverage by 0.06%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2534      +/-   ##
==========================================
+ Coverage   84.67%   84.74%   +0.06%     
==========================================
  Files          93       93              
  Lines        9301     9309       +8     
  Branches     2096     2097       +1     
==========================================
+ Hits         7876     7889      +13     
+ Misses        940      937       -3     
+ Partials      485      483       -2     

Impacted Files	Coverage Δ
vyper/old_codegen/expr.py	80.00% <100.00%> (+0.12%)	⬆️
vyper/old_codegen/external_call.py	94.33% <0.00%> (ø)
vyper/old_codegen/parser_utils.py	83.01% <0.00%> (+0.23%)	⬆️
vyper/builtin_functions/functions.py	88.96% <0.00%> (+0.33%)	⬆️
vyper/ast/nodes.py	93.95% <0.00%> (+0.36%)	⬆️

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