Make local functions static where applicable

[sharwell]

No description provided.

[codemzs]

[codecov]

Codecov Report

Merging #4530 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #4530      +/-   ##
==========================================
+ Coverage    75.1%   75.11%   +<.01%     
==========================================
  Files         908      908              
  Lines      160260   160260              
  Branches    17259    17259              
==========================================
+ Hits       120369   120385      +16     
+ Misses      35070    35061       -9     
+ Partials     4821     4814       -7

Flag	Coverage Δ
#Debug	75.11% <ø> (ø)	⬆️
#production	70.52% <ø> (+0.01%)	⬆️
#test	90.26% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
....ML.Data/DataLoadSave/LegacyCompositeDataLoader.cs	83.12% <ø> (ø)	⬆️
test/Microsoft.ML.Functional.Tests/ModelFiles.cs	96.26% <ø> (ø)	⬆️
...icrosoft.ML.Functional.Tests/DataTransformation.cs	100% <ø> (ø)	⬆️
...est/Microsoft.ML.Tests/Transformers/ConcatTests.cs	91.81% <ø> (ø)	⬆️
...L.AutoML/TrainerExtensions/TrainerExtensionUtil.cs	85.15% <0%> (-1.75%)	⬇️
src/Microsoft.ML.Transforms/Text/LdaTransform.cs	84.44% <0%> (-0.16%)	⬇️
src/Microsoft.ML.AutoML/Sweepers/Parameters.cs	83.89% <0%> (+0.84%)	⬆️
src/Microsoft.ML.Maml/MAML.cs	26.21% <0%> (+1.45%)	⬆️
....ML.AutoML/PipelineSuggesters/PipelineSuggester.cs	86.55% <0%> (+6.72%)	⬆️
...c/Microsoft.ML.FastTree/Utils/ThreadTaskManager.cs	100% <0%> (+20.51%)	⬆️