Fix: export method getArgsTypeList for extension

[LaurenceLiZhixin]

What this PR does:

Which issue(s) this PR fixes:
Fixes #

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• All ut passed (run 'go test ./...' in project root)
• After go-fmt ed , run 'go fmt project' using goland.
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• After import formatted, (using imports-formatter to run 'imports-formatter .' in project root, to format your import blocks, mentioned in CONTRIBUTING.md above)
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[codecov-commenter]

Codecov Report

Merging #1913 (e5e2efa) into 3.0 (a0528f2) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              3.0    #1913   +/-   ##
=======================================
  Coverage   44.95%   44.95%           
=======================================
  Files         287      287           
  Lines       17130    17130           
=======================================
  Hits         7701     7701           
- Misses       8616     8617    +1     
+ Partials      813      812    -1     

Impacted Files	Coverage Δ
protocol/dubbo/impl/hessian.go	32.88% <100.00%> (ø)
metrics/prometheus/reporter.go	33.33% <0.00%> (-1.70%)	⬇️
filter/metrics/filter.go	100.00% <0.00%> (+15.00%)	⬆️

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