Move IDataView into Microsoft.ML namespace

[eerhardt]

Fix #2974

Here's the steps I took:

1. Rename the folders and files for the src\Microsoft.Data.DataView and pkg\Microsoft.Data.DataView to Microsoft.ML.DataView.
2. Rename the namespaces in that assembly:
   • IDataView.cs and DataViewSchema.cs move to the Microsoft.ML namespace.
   • Everything else in the assembly move to the Microsoft.ML.Data namespace.
3. Find all using Microsoft.Data.DataView; lines and delete them.
4. Compile, and fix any build errors to add using Microsoft.ML.Data; lines.
5. In the Parquet files, there were some full namespace usages that I removed.
6. Find all "Microsoft.Data" in the repo, and change as appropriate (it was only docs).
   • there is only 1 place left - which was there before we made this change

machinelearning/src/Microsoft.ML.Core/ComponentModel/AssemblyLoadingUtils.cs

Line 121 in 87ede9e

"microsoft.data.",

[codecov]

Codecov Report

Merging #2987 into master will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2987      +/-   ##
==========================================
- Coverage    72.3%   72.27%   -0.03%     
==========================================
  Files         796      802       +6     
  Lines      142349   142865     +516     
  Branches    16051    16129      +78     
==========================================
+ Hits       102923   103254     +331     
- Misses      35041    35193     +152     
- Partials     4385     4418      +33

Flag	Coverage Δ
#Debug	72.27% <100%> (-0.03%)	⬇️
#production	68% <100%> (-0.02%)	⬇️
#test	88.48% <ø> (ø)	⬆️

Impacted Files	Coverage Δ
src/Microsoft.ML.Core/Data/RootCursorBase.cs	100% <ø> (ø)	⬆️
...t.ML.Mkl.Components/SymSgdClassificationTrainer.cs	74.69% <ø> (ø)	⬆️
src/Microsoft.ML.Data/Transforms/SkipTakeFilter.cs	88.33% <ø> (ø)	⬆️
...osoft.ML.Data/DataLoadSave/DataLoaderExtensions.cs	100% <ø> (ø)	⬆️
...rc/Microsoft.ML.Data/EntryPoints/EntryPointNode.cs	68.58% <ø> (ø)	⬆️
src/Microsoft.ML.FastTree/FastTreeRanking.cs	48.19% <ø> (ø)	⬆️
...c/Microsoft.ML.Data/DataView/LambdaColumnMapper.cs	63.02% <ø> (ø)	⬆️
...osoft.ML.Data/DataLoadSave/Binary/UnsafeTypeOps.cs	71.55% <ø> (ø)	⬆️
...t.ML.Data/DataLoadSave/Text/LoadColumnAttribute.cs	100% <ø> (ø)	⬆️
...StandardTrainers/Standard/StochasticTrainerBase.cs	88.37% <ø> (ø)	⬆️
... and 382 more

[TomFinley]

Whew... thanks for doing this Eric!

[Ivanidzo4ka]