Installer: add simpler way to specify Visual Studio location

[josetr]

[codecov[bot]]

Codecov Report

Merging #22 into master will not change coverage. The diff coverage is 100%.

@@           Coverage Diff           @@
##           master      #22   +/-   ##
=======================================
  Coverage   78.74%   78.74%           
=======================================
  Files          27       27           
  Lines         701      701           
  Branches       72       72           
=======================================
  Hits          552      552           
  Misses        109      109           
  Partials       40       40

Impacted Files	Coverage Δ
...rc/VsixTesting.Xunit/Internal/VsTestCaseFactory.cs	87.14% <100%> (ø)	:arrow_up:

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