refactor[lang]: refactor decorator parsing

[charles-cooper]

What I did

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Commit message

minor refactor of decorator parsing, which simplifies the code and
should make it easier to add new builtin decorators in the future

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.16%. Comparing base (efdfa7f) to head (32f2cb3).
Report is 88 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4490      +/-   ##
==========================================
+ Coverage   92.11%   92.16%   +0.04%     
==========================================
  Files         122      122              
  Lines       17455    17475      +20     
  Branches     2961     2962       +1     
==========================================
+ Hits        16079    16105      +26     
+ Misses        962      958       -4     
+ Partials      414      412       -2     

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[cyberthirst]

didn't look into it closely, but can't we use the new machinery in from_InterfaceDef as well?

[charles-cooper]

didn't look into it closely, but can't we use the new machinery in from_InterfaceDef as well?

no, those have a different machinery since functions in interface declarations don't use decorators