Add ResolveResponseStatus function to help middleware/handlers determine HTTP status code and echo.Response

[aldas]

Add ResolveResponseStatus function to help middleware/handlers determine HTTP status code and echo.Response.

Loggers and tracing middlewares need to determine status code from either from error or echo.Response. Also - response is needed often for knowing response size from echo.Response.Size. so this function tries to shorten these 2 requirements.

Relates to labstack/echo-contrib#141
and https://github.com/labstack/echo-contrib/blob/master/internal/helpers/statuscode.go

also #2892

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.01%. Comparing base (4dd9f46) to head (19364e2).
⚠️ Report is 8 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2900      +/-   ##
==========================================
+ Coverage   92.94%   93.01%   +0.07%     
==========================================
  Files          43       43              
  Lines        4491     4496       +5     
==========================================
+ Hits         4174     4182       +8     
+ Misses        197      196       -1     
+ Partials      120      118       -2     

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