Pick up new CoreFX packages and abandon old ones

[wtgodbe]

This change does a few things:

• Separates our external dependencies into external/project.json
• Changes all dependencies on System.xyz to Microsoft.Private.CoreFx.NETCoreApp
• Removes several JIT/config project.json files (Everything except benchmark, benchmark+roslyn, benchmark+serialize), and re-assigns all test projects who previously depended on those, to depend on test-dependencies/project.json
• Adds external.depproj, which handles restoring dependencies from external/project.json into a Targeting Pack folder, which tests reference directly.
• Moves from netcoreapp1.1 to netcoreapp2.0, where possible.

There's a lot of changes here, but the relevant files should be at the top of the changeset - everything else is either a deletion of a project.json file, or a deletion of a Property referencing one of those files. (Or @AndyAyersMS fixing a bad ReferencePath in an .ilproj).

I did not touch any of the Perf stuff, as those tests still depend on using NetStandard1.4. Once that changes, we should be able to get rid of those project.json's as well, and point perf tests at test-dependencies/project.json.

[wtgodbe]

CC @gkhanna79 @jkotas @ramarag @mellinoe @AndyAyersMS @DrewScoggins @weshaggard @ericstj

[wtgodbe]

CC @pgavlin as well, for the JIT stuff

[gkhanna79]

Is the Pri1 test build and run clean with it locally and (clean run) in Helix?

[wtgodbe]

@gkhanna79 I sent a few jobs to helix that came back clean, but haven't done a full pri-1 job yet - I'm setting that up now

[ericstj]

This package is not needed.

[ericstj]

This is not needed.

[ericstj]

You may need some additional package refs. We still produce packages for those listed here: https://github.com/dotnet/versions/blob/master/build-info/dotnet/corefx/master/Latest_Packages.txt. Some of those overlap with NETCore.App but there is more than just S.R.CS.Unsafe that does not.

[mellinoe]

LGTM. We can add the extra package references now, or later when folks start wanting to use them. As long as the current suite of tests is satisfied then that seems ok to me.

[wtgodbe]

@gkhanna79 @weshaggard @ericstj has the UnicodeEncoding class changed recently? Looks like https://github.com/dotnet/coreclr/blob/master/tests/src/CoreMangLib/cti/system/text/unicodeencoding/unicodeencodinggetbytecount1.cs#L192 may need to change, based on the current errors.

Also, with the changes from #10150, tests are passing in Helix.

[wtgodbe]

@dotnet-bot test OSX x64 Checked Build and Test

[jkotas]

I have changed UnicodeEncoding in #10124 . The CI was green with my change. Is this running more tests?

[jkotas]

https://github.com/dotnet/coreclr/blob/master/tests/src/CoreMangLib/cti/system/text/unicodeencoding/unicodeencodinggetbytecount1.cs#L192

Yes, it needs to change. It is build break caused by adding a new API. It is expected - it was discussed during the review and determined to be ok.

[wtgodbe]

@jkotas what should it be changed to?

[jkotas]

(char[])null, 0, 0. Or delete the test - there is redundant test in corefx with much more comprehensive coverage.

[wtgodbe]

I'll just insert the fix for now.

[AndyAyersMS]

Fixes for the odd path corruptions I introduced look good (at least a sampling of them). Thanks for fixing this.