This is a fairly large change to our build infrastructure that does several key/important things.

Overview

General

1. Remove all dependencies on BuildTools
2. Updates our dotnet sdk to the latest 3.0 preview4 sdk
3. Imports and uses the arcade SDK

build.sh/build.cmd

1. Changes all the managed components, SPC, SOS, package restore to use SDK style projects and import arcade
2. Changes our output location from bin/Product/${__BuildOS}.${__BuildArch}.${__BuildConfig} to artifacts/Product/${__BuildOS}/${__BuildArch}/${__BuildConfig}
3. Updates our native components to reference the new output locations

build-test.sh/build-test.cmd

1. Change our tests to build as SDK style projects
2. Change the traversal logic to use the built in multi-project build solution provided by the dotnet sdk, which is sln files with project references.
3. Due to the sln files requiring unique test names, several dozen tests have been renamed from either lib.csproj or test.csproj to their parent directories name.

Remaining work

This PR is accurately a work in progress, building both the product and the tests complete; however, the following are still not working:

1. Creating the Core_Root
   a. This should only require a default build target to depend on the existing runtest.proj targets.
2. Changes to runtest.py to use the artifact directory
3. Changes to helix publish to use the artifact directory
4. Documentation changes:
   a. The usage of sln files will change our addition of tests to the repository.
   b. Now in order to add a test, a dotnet sdk command will need to be called. An example call to add a test would be ~/coreclr/.dotnet/dotnet sln tests/src/priority_0-1.sln JIT/Regression/newTest/newTest.csproj

The following is not investigated, and will probably require more work:

1. Changes to signing to either use the artifacts directory, or rely on the built in signing of the arcade sdk
2. Version.h/c has been changed, we should change the sem ver2 and directly use the arcade SDK to create the version information for the native components.

Cleanup work

The following would be nice to have cleanup work that is enabled by this change:

1. Removal of dir.props, this have been superseded by Directory.Build.props
2. Removal of dir.targets, this has been superseded by Directory.Build.targets