Fix MSTest filter syntax

[vincentleungrsm]

Previously needed dotnet test --filter "TestCase.FullyQualifiedName=FailingTest.When_adding_two_numbers::should_be_greater_than_ten"

Now matches MSTest filter syntax dotnet test --filter "FullyQualifiedName=FailingTest.When_adding_two_numbers::should_be_greater_than_ten"

Related: #495

[vincentleungrsm]

PR: machine/machine.specifications.runner.visualstudio#175

(apologies I'm unfamiliar with how to connect PRs to issues in github)

[jsskeen-utah]

This would be great to merge (or at least have fixed). I just spent about an hour trying to get dotnet test --filter "FullyQualifiedName~MyClass" to work, only to find that you have to add TestCase., which was not even hinted at through a lot of web searching and AI chats. All the mainstream dotnet test runners don't require that prefix on the filter, so it becomes quite an obscure issue if you run into it.