housekeeping: Added Splat adapter tests

[RLittlesII]

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
Resolves: #287

• Added additional Autofac tests
• Added additional DryIoc tests
• Made DryIocDependencyResolver methods virtual

What might this PR break?

DryIoc Adapter

Please check if the PR fulfills these requirements

• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

[codecov]

Codecov Report

Merging #309 into master will increase coverage by 0.42%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #309      +/-   ##
==========================================
+ Coverage   70.18%   70.61%   +0.42%     
==========================================
  Files          61       61              
  Lines        3515     3515              
  Branches      312      312              
==========================================
+ Hits         2467     2482      +15     
+ Misses       1007      992      -15     
  Partials       41       41

Impacted Files	Coverage Δ
src/Splat.DryIoc/DryIocDependencyResolver.cs	56.25% <100%> (+34.37%)	⬆️
.../Splat/ServiceLocation/DependencyResolverMixins.cs	72% <0%> (+4%)	⬆️
src/Splat.Autofac/AutofacDependencyResolver.cs	41.17% <0%> (+5.88%)	⬆️
src/Splat.Autofac/SplatAutofacExtensions.cs	100% <0%> (+50%)	⬆️

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