Remove startup overhead caused by enumerating all assemblies for callsite logic

[snakefoot]

NetStandard2 is capable of hiding the LoggerFactory-assembly, and the Microsoft.Extensions.Logging.Filter only works for NetCore1.

When calling UseNLog or AddNLogWeb then NLog.Web.AspNetCore will ensure to "hide" itself.

[codecov-io]

Codecov Report

Merging #485 (e901fc7) into master (80d7d59) will decrease coverage by 0.13%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #485      +/-   ##
==========================================
- Coverage   81.15%   81.02%   -0.14%     
==========================================
  Files          14       14              
  Lines        1279     1254      -25     
  Branches      215      211       -4     
==========================================
- Hits         1038     1016      -22     
+ Misses        165      164       -1     
+ Partials       76       74       -2     

Impacted Files	Coverage Δ
...tensions.Hosting/Extensions/ConfigureExtensions.cs	83.87% <100.00%> (+0.53%)	⬆️
...g.Extensions.Logging/Logging/NLogLoggerProvider.cs	98.27% <100.00%> (+3.03%)	⬆️

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[codecov-commenter]

Codecov Report

Merging #485 (00ffa03) into master (87007d8) will decrease coverage by 0.14%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #485      +/-   ##
==========================================
- Coverage   79.95%   79.81%   -0.15%     
==========================================
  Files          17       17              
  Lines        1452     1427      -25     
  Branches      236      233       -3     
==========================================
- Hits         1161     1139      -22     
+ Misses        184      183       -1     
+ Partials      107      105       -2     

Impacted Files	Coverage Δ
...tensions.Hosting/Extensions/ConfigureExtensions.cs	85.71% <100.00%> (+0.42%)	⬆️
...g.Extensions.Logging/Logging/NLogLoggerProvider.cs	98.27% <100.00%> (+3.03%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 87007d8...00ffa03. Read the comment docs.