fix codegen failure with nonreentrant keys

[charles-cooper]

codegen now fails (stops compiling) as of eae0eaf. This is because
the storage layout is generated correctly but the type metadata is not
updated after the first function that references a nonreentrancy key.

This commit also adds a codegen test to check codegen of repeated
nonreentrancy keys.

What I did

Fix bug introduced in #2439

How I did it

How to verify it

Check the following contract fails to compile on master but compiles on this branch

@external
@nonreentrant("foo")
def foo():
    pass
 
@external
@nonreentrant("foo")
def bar():
    pass

Description for the changelog

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[codecov-commenter]

Codecov Report

Merging #2514 (efe4666) into master (4b9d860) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2514      +/-   ##
==========================================
- Coverage   84.62%   84.61%   -0.02%     
==========================================
  Files          94       94              
  Lines        9303     9328      +25     
  Branches     2099     2103       +4     
==========================================
+ Hits         7873     7893      +20     
- Misses        943      946       +3     
- Partials      487      489       +2     

Impacted Files	Coverage Δ
vyper/semantics/validation/data_positions.py	93.75% <100.00%> (+0.64%)	⬆️
vyper/builtin_functions/functions.py	88.68% <0.00%> (-0.29%)	⬇️
vyper/old_codegen/parser_utils.py	82.78% <0.00%> (ø)

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