fix: prevent enum members to have unexpected structures

[trocher]

What I did

• Fixed enum members can have unexpected structure #3239
• Added the node of the enum declaration to the exception raised when it is empty to indicate its location.

How I did it

Added checks that the fields of an enum must be Expr statements with values that are Name

How to verify it

See tests

Commit message

fix: prevent enum members to have unexpected structures

Description for the changelog

Enforce enum members to be simple names

Cute Animal Picture

[fubuloubu]

I'll let @charles-cooper set auto-merge and/or approve this one

[codecov-commenter]

Codecov Report

Merging #3240 (851bf55) into master (d4f04c6) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3240   +/-   ##
=======================================
  Coverage   88.94%   88.94%           
=======================================
  Files          84       84           
  Lines       10588    10590    +2     
  Branches     2208     2209    +1     
=======================================
+ Hits         9417     9419    +2     
  Misses        760      760           
  Partials      411      411           

Impacted Files	Coverage Δ
vyper/semantics/types/user.py	85.57% <100.00%> (+0.09%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more