[AspNetCore] Avoid boxing of status code tags

[CodeBlanch]

Changes

• Use a dictionary of pre-boxed status code values to avoid boxing perf hit on every request. Borrowed from AspNetCore's upcoming metric support.

Merge requirement checklist

• CONTRIBUTING guidelines followed (nullable enabled, static analysis, etc.)
• Appropriate CHANGELOG.md files updated for non-trivial changes

[reyang]

@vishweshbankwar FYI

[codecov]

Codecov Report

Merging #4360 (0fe5fdf) into main (6918866) will increase coverage by 0.08%.
The diff coverage is 98.66%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4360      +/-   ##
==========================================
+ Coverage   84.77%   84.85%   +0.08%     
==========================================
  Files         298      299       +1     
  Lines       11984    12057      +73     
==========================================
+ Hits        10159    10231      +72     
- Misses       1825     1826       +1     

Impacted Files	Coverage Δ
...ation.AspNetCore/Implementation/TelemetryHelper.cs	98.63% <98.63%> (ø)
...tation.AspNetCore/Implementation/HttpInListener.cs	90.30% <100.00%> (ø)
...AspNetCore/Implementation/HttpInMetricsListener.cs	74.35% <100.00%> (ø)

... and 4 files with indirect coverage changes