Update NLog to improve local log decoration coverage

[jaffinito]

Description

Changes how the NLog instrumentation updates the log message for local log decoration.

• Instead of examining and using LogEventInfo.Message, the new instrumentation uses LogEventInfo.FormattedMessage and its backing field, (v4.5+ _formattedMessage)|(Pre v4.5 formattedMessage). This property has additional logic that Message does not and appears to be the source for the actual log message we see. Calling FormattedMessage causes NLog to build the message and store it in the backing field.
• Using the visibility bypasser, we get the setter for the backing field and use it to set the field to itself with our decoration token. The Action is stored staticly, same as with other bypasser setups.
• Since we can only get the major assembly version from NLog assembly we cannot use minVersion or maxVersion. The cleanest solution was to check for _formattedMessage first since it is the going forward name and if that fails, use formattedMessage. This is done using reflection, but is will only happen once per run so the impact is minimal.

Caveats:
This does not 100% cover all the log lines. It does cover the vast majority of them.

Author Checklist

• Unit tests, Integration tests, and Unbounded tests completed
• Performance testing completed with satisfactory results (if required)
• Agent Changelog or Lambda Agent changelog updated

Reviewer Checklist

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

[codecov-commenter]

Codecov Report

Merging #1393 (e7f2ffe) into main (670936f) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1393      +/-   ##
==========================================
- Coverage   71.62%   71.61%   -0.01%     
==========================================
  Files         459      459              
  Lines       30619    30619              
==========================================
- Hits        21932    21929       -3     
- Misses       8687     8690       +3     

Impacted Files	Coverage Δ
src/Agent/NewRelic/Agent/Core/Time/Scheduler.cs	79.45% <0.00%> (-2.06%)	⬇️

[nrcventura]

It sounds like there are integration tests that exercise this code, but we need an item on our backlog to add the necessary assertions to validate this behavior.

[jaffinito]

I added a story to our backlog.