HttpStatusCode as int instead of string

[cijothomas]

Fixes part of #940

Part 2 of #954

Changes

HttpStatusCode in all spans attribute (http.status_code) to use int value.

Please provide a brief description of the changes here. Update the
CHANGELOG.md for non-trivial changes.

For significant contributions please make sure you have completed the following items:

• Design discussion issue #
• Changes in public API reviewed

[codecov]

Codecov Report

Merging #998 into master will increase coverage by 0.01%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master     #998      +/-   ##
==========================================
+ Coverage   68.17%   68.18%   +0.01%     
==========================================
  Files         218      218              
  Lines        5973     5975       +2     
  Branches      974      974              
==========================================
+ Hits         4072     4074       +2     
  Misses       1630     1630              
  Partials      271      271              

Impacted Files	Coverage Δ
...umentation.AspNet/Implementation/HttpInListener.cs	0.00% <0.00%> (ø)
...strumentation.Http/Implementation/HttpTagHelper.cs	92.85% <ø> (-0.90%)	⬇️
src/OpenTelemetry.Api/Trace/SpanContext.cs	60.00% <50.00%> (ø)
...etry.Api/Context/Propagation/TraceContextFormat.cs	49.57% <100.00%> (ø)
....Jaeger/Implementation/JaegerActivityExtensions.cs	84.61% <100.00%> (+0.11%)	⬆️
...tation.AspNetCore/Implementation/HttpInListener.cs	77.21% <100.00%> (ø)
...tp/Implementation/HttpHandlerDiagnosticListener.cs	71.23% <100.00%> (ø)
src/OpenTelemetry/Context/Propagation/B3Format.cs	65.78% <100.00%> (ø)
src/OpenTelemetry/Trace/ActivitySourceAdapter.cs	94.87% <100.00%> (+0.75%)	⬆️

[cijothomas]

Ofcourse this breaks all exporters except console, as they aren't looking for activity.TagObjects :) Exporter changes are coming next.

[reyang]

LGTM.