ILoggingBuilder AddNLog extension method with correct dispose and no double logging

[snakefoot]

Resolves #324 for ILoggingBuilder. But will NOT help #254 for ILoggerFactory.

Fixes lifetime issue found in NLog/NLog#3284 where calling ILoggingBuilder.AddNLog caused NLogLoggingProvider not being disposed correctly on application shutdown (No flush and shutdown).

[snakefoot]

Should probably also make a PR for NLog.Web.AspNetCore so it will also work correctly there.

[codecov-io]

Codecov Report

Merging #325 into master will increase coverage by 0.5%.
The diff coverage is 87.5%.

@@            Coverage Diff            @@
##           master     #325     +/-   ##
=========================================
+ Coverage   81.05%   81.56%   +0.5%     
=========================================
  Files          12       12             
  Lines        1098     1101      +3     
  Branches      193      194      +1     
=========================================
+ Hits          890      898      +8     
+ Misses        143      139      -4     
+ Partials       65       64      -1

Impacted Files	Coverage Δ
...tensions.Hosting/Extensions/ConfigureExtensions.cs	93.1% <100%> (+1.1%)	⬆️
...tensions.Logging/Extensions/ConfigureExtensions.cs	31.14% <50%> (+0.5%)	⬆️
...g.Extensions.Logging/Logging/NLogLoggerProvider.cs	95.77% <0%> (+5.63%)	⬆️

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[snakefoot]

@304NotModified Milestone has to be 1.5.4. See also: https://www.nuget.org/packages/NLog.Extensions.Logging/1.5.3

[304NotModified]

@304NotModified Milestone has to be 1.5.4. See also: https://www.nuget.org/packages/NLog.Extensions.Logging/1.5.3

Sharp! Thanks! 1.5.3 milestone/github release fixed!

[snakefoot]

Created NLog/NLog.Web#459 for NLog.Web.AspNetCore (waits for the 1.5.4 release)

[304NotModified]

👍