Move common test assets out of Azure Application Configuration

[conniey]

This is part of a couple PRs. This PR:

• Creates a "azure-common-test" package.
• Deletes a lot of unnecessary "factory" classes and delay providers that are not necessary.
  • The delay providers in tests can be done with reactor's VirtualTimeScheduler. We don't have to roll our own.
  • The TestName factories were just returning an instance of the class itself. 🤔 Wasn't abstracting any object creation.
• Removes a lot of static creation methods and static context methods.
  • Having one static SdkContext, TestResourceNamer, etc. will make it impossible to run test classes in parallel.
• Creates a TestBase class.

Related to #3208.

[azuresdkci]

Can one of the admins verify this patch?

[alzimmermsft]

Given these

[alzimmermsft]

Should we also add placeholders for BeforeClass and AfterClass? These could allow performance wins with the tests instead of having to instantiate common build for every test.

[conniey]

I thought about it, but the existing TestBase had a BeforeClass and AfterClass that didn't add value. I'm not sure how performance could be improved with having the base class with a no-op BeforeClass that then calls the implementing class.

[alzimmermsft]

That was left a little too vague on my part, less on the stub methods being useful now but more on they would allow optimizations. For example the App Config unit tests create a new builder, run an authenticate credentials, and construct a new client for each test. That could just get done once during the beforeClass call.

[conniey]

Ahh I see what you're saying. Looking into the BeforeClass annotation... unfortunately it has to be a static method. So, it doesn't lend itself to having a stub method that can be overridden in an implementing class. :/

[JonathanGiles]

LGTM - just a package rename suggestion