**DRAFT** fix: Better null handling during ASP.NET Core 6+ browser agent injection.

[tippmar-nr]

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Description

Adds additional null handling and exception handling code for ASP.NET Core 6+ browser agent injection.
Also adds additional checking as early as possible to short-circuit around the browser injection if we aren't supposed to inject the script due to configuration or response content type and path.

Author Checklist

• Unit tests, Integration tests, and Unbounded tests completed
• Performance testing completed with satisfactory results (if required)

Reviewer Checklist

• Perform code review
• Pull request was adequately tested (new/existing tests, performance tests)

[codecov-commenter]

Codecov Report

Merging #2037 (575b9c9) into main (ca96d0c) will decrease coverage by 0.04%.
Report is 1 commits behind head on main.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #2037      +/-   ##
==========================================
- Coverage   81.07%   81.04%   -0.04%     
==========================================
  Files         394      394              
  Lines       24667    24671       +4     
  Branches     2962     2963       +1     
==========================================
- Hits        20000    19994       -6     
- Misses       3883     3893      +10     
  Partials      784      784              

Files	Coverage Δ
src/Agent/NewRelic/Agent/Core/Agent.cs	70.64% <0.00%> (-0.93%)	⬇️

... and 3 files with indirect coverage changes