For all templates that have tests, add support for MSTest, and TUnit in addition to xUnit v3.

• Create separate test files for each of the target framework
• All test classes should contain tests covering the same code, with the only difference being the test framework
• Conditionally include the correct NuGet packages based on the selected test framework.
• Replace the --no-tests template option with a --tests option that accepts values tunit, mstest, xunit, or none
• Only include tests that match the requested framework
• When none is selected, don't include a testing project