Extract IDataView into its own assembly and NuGet package

[eerhardt]

Moving IDataView and related types into a new library: Microsoft.Data.DataView

Fix #1860

I've split the changes into 3 commits for easy reviewing:

1. Copy the files out into the new folder with minimal/zero changes
2. Get the new assembly building
   3 Get ML.NET building on the new assembly

[sfilipi]

[yaeldekel]

namespace Microsoft.ML.Data

Will the namespace still have "ML" in it?

---

Refers to: src/Microsoft.Data.DataView/IDataView.cs:9 in 33c8cec. [](commit_id = 33c8cec, deletion_comment = False)

[eerhardt]

Will the namespace still have "ML" in it?

Sorry, I should have commented on this originally. My initial implementation is just to move the types in the same namespace. Then the next change is to move namespaces. Since that is going to affect a huge number of files, I wanted to put that in its own PR for easy reviewing.

I am also considering supporting more TFMs in the new library (net45 and netstandard1.x) so it can get as far of reach as possible. That will be a future PR as well.

[yaeldekel]

[codecov]

Codecov Report

Merging #2220 into master will decrease coverage by <.01%.
The diff coverage is 80.18%.

@@            Coverage Diff             @@
##           master    #2220      +/-   ##
==========================================
- Coverage   69.78%   69.78%   -0.01%     
==========================================
  Files         786      783       -3     
  Lines      143945   143438     -507     
  Branches    16648    16588      -60     
==========================================
- Hits       100451   100094     -357     
+ Misses      38951    38813     -138     
+ Partials     4543     4531      -12

Flag	Coverage Δ
#Debug	69.78% <80.18%> (-0.01%)	⬇️
#production	66.11% <79.9%> (-0.02%)	⬇️
#test	84.92% <100%> (ø)	⬆️

[TomFinley]

Feels wrong to not have Contracts.Assert and Check on IDataView... it's growing up... 😄 Thanks @eerhardt