Idiomatic Test Organization

[danfiedler-msft]

The new code organization in #476 paves the way for this repository to move towards more idiomatic .NET unit tests. For example:

• source and tests in different directories
• one test project for each assembly under test (i.e., Shared.CLI.Tests for the Shared.CLI project and Shared.Lib.Tests for the Shared.Lib project.)
• test code organization mirroring the assembly under test (e.g., Shared.CLI.Tests.Tools.DefoggerToolTestsrather than Microsoft.CST.OpenSource.Tests.DefoggerTests`)
• isolating integration tests to a separate test assembly