fix[lang]: typecheck hashmap indexes with folding

[DanielSchiavini]

Fixes #3984

What I did

• Updated index checks for when the subscript is folded

How I did it

• Use the reduced (i.e. folded) value when checking the index type

How to verify it

• Tests are included

Commit message

this commit fixes a bug in typechecking of folded values for hashmap
indexes. there was previously a carveout for subscript typechecking for
arrays; however, it should not apply to hashmap indexes.

this was introduced as an edge case resulting from the semantic changes
in 56c4c9dbc0. a related fix was applied in 75fb0594ab3, but it did not
handle hashmaps.

Description for the changelog

HashMap index is checked when the subscript is folded

Cute Animal Picture

[charles-cooper]

this looks good to me. paging @Leminkay to double check

[Leminkay]

LGTM!

[charles-cooper]

@DanielSchiavini update the commit message please with a description of how the change was arrived at, and i'll merge

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 47.96%. Comparing base (4c66c8c) to head (93d1bb7).

❗ Current head 93d1bb7 differs from pull request most recent head 19e927a. Consider uploading reports for the commit 19e927a to get more accurate results

Files	Patch %	Lines
vyper/semantics/analysis/local.py	0.00%	4 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff             @@
##           master    #4007       +/-   ##
===========================================
- Coverage   90.90%   47.96%   -42.94%     
===========================================
  Files         105      105               
  Lines       15246    15247        +1     
  Branches     3358     3358               
===========================================
- Hits        13859     7313     -6546     
- Misses        952     7326     +6374     
- Partials      435      608      +173     

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