fix(scope-manager): correctly reference generic parameters when decorator metadata is enabled

[bradzacher]

Fixes #2972

[typescript-eslint]

Thanks for the PR, @bradzacher!

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[codecov]

Codecov Report

Merging #2975 (f419577) into master (957523c) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2975   +/-   ##
=======================================
  Coverage   92.74%   92.74%           
=======================================
  Files         313      313           
  Lines       10636    10639    +3     
  Branches     3017     3018    +1     
=======================================
+ Hits         9864     9867    +3     
  Misses        353      353           
  Partials      419      419           

Flag	Coverage Δ
unittest	92.74% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
...kages/scope-manager/src/referencer/ClassVisitor.ts	91.89% <100.00%> (+0.22%)	⬆️