feat: Add support for Serilog.Extensions.Logging and NLog.Extensions.Logging

[chynesNR]

Previously, if we detected Microsoft.Extensions.Logging and another logger, we would only instrument MEL, in order to avoid double collection of logs. This turned out to be a flawed approach, because MEL does not store any context data. It relies on the underlying logger to handle it. So now, if we detect that scenario, we disable MEL instrumentation. Only if we don't find another logger that we know how to instrument, will we instrument MEL.

In order for us to collect context data from an ILogger via MEL, the logger must implement IExternalScopeProvider (specifically the ForEachScope function). Scope data can be any object, but we will only collect it if it's a key-value pair (or collection of key-value pairs). This is how NLog and Serilog implement their scope provider, so this seems like a reasonable restriction.

I also found that NLog treats context data and scope data differently. We weren't recording NLog's scope data at all before; now we are.

Addresses #1859

Author Checklist

• Unit tests, Integration tests, and Unbounded tests completed

Reviewer Checklist

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

[nr-ahemsath]

Looks good! I appreciate all of the comments to help understand what is going on. 👍

[codecov-commenter]

Codecov Report

Merging #1860 (3c7c667) into main (6524915) will decrease coverage by 0.13%.
Report is 3 commits behind head on main.
The diff coverage is 44.44%.

@@            Coverage Diff             @@
##             main    #1860      +/-   ##
==========================================
- Coverage   83.57%   83.44%   -0.13%     
==========================================
  Files         389      402      +13     
  Lines       24504    24670     +166     
==========================================
+ Hits        20478    20586     +108     
- Misses       4026     4084      +58     

Files Changed	Coverage Δ
.../NewRelic.Agent.Extensions/Logging/LogProviders.cs	0.00% <0.00%> (ø)
....Agent.Extensions/Reflection/VisibilityBypasser.cs	89.26% <100.00%> (+0.21%)	⬆️

... and 21 files with indirect coverage changes