Add tests for IParameterValue implementations

[sharwell]

This change provides deterministic coverage for the implementation of LongParameterValue, FloatParameterValue, and StringParameterValue.

[codecov]

Codecov Report

Merging #4549 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4549      +/-   ##
==========================================
+ Coverage   75.13%   75.14%   +<.01%     
==========================================
  Files         908      908              
  Lines      160238   160289      +51     
  Branches    17256    17256              
==========================================
+ Hits       120401   120442      +41     
- Misses      35016    35031      +15     
+ Partials     4821     4816       -5

Flag	Coverage Δ
#Debug	75.14% <100%> (ø)	⬆️
#production	70.52% <ø> (-0.02%)	⬇️
#test	90.34% <100%> (+0.02%)	⬆️

Impacted Files	Coverage Δ
test/Microsoft.ML.AutoML.Tests/SweeperTests.cs	59.17% <100%> (+17.64%)	⬆️
src/Microsoft.ML.Core/Data/ProgressReporter.cs	70.95% <0%> (-6.99%)	⬇️
...rosoft.ML.AutoML/ColumnInference/TextFileSample.cs	59.6% <0%> (-2.65%)	⬇️
src/Microsoft.ML.Maml/MAML.cs	24.75% <0%> (-1.46%)	⬇️
...soft.ML.TestFramework/DataPipe/TestDataPipeBase.cs	76.47% <0%> (+0.39%)	⬆️
...soft.ML.Data/DataLoadSave/Text/TextLoaderCursor.cs	85.31% <0%> (+0.6%)	⬆️
src/Microsoft.ML.AutoML/Sweepers/Parameters.cs	84.32% <0%> (+1.27%)	⬆️
...L.AutoML/TrainerExtensions/TrainerExtensionUtil.cs	86.89% <0%> (+1.74%)	⬆️
test/Microsoft.ML.AutoML.Tests/DatasetUtil.cs	91.3% <0%> (+2.6%)	⬆️

[justinormont]

LGTM