fix alias type of generic with multi formal params

[sdghchj]

Describe the PR
fix bug: alias type of generc with multi formal params

Relation issue
#1489

[codecov]

Codecov Report

Patch coverage: 86.66% and no project coverage change.

Comparison is base (aa3e8d5) 85.14% compared to head (c76afc6) 85.15%.

❗ Current head c76afc6 differs from pull request most recent head de02797. Consider uploading reports for the commit de02797 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1505   +/-   ##
=======================================
  Coverage   85.14%   85.15%           
=======================================
  Files          19       19           
  Lines        3616     3630   +14     
=======================================
+ Hits         3079     3091   +12     
- Misses        459      460    +1     
- Partials       78       79    +1     

Impacted Files	Coverage Δ
gen/gen.go	93.51% <ø> (ø)
field_parser.go	96.90% <33.33%> (-0.55%)	⬇️
generics.go	100.00% <100.00%> (ø)
operation.go	96.11% <100.00%> (+0.01%)	⬆️
parser.go	94.50% <100.00%> (+0.05%)	⬆️

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