Only run blocking interceptors for blocking tests, and suspending for suspending

[JakeWharton]

A similar case that'd be nice to support is something like:

class SuspendingInterceptor : CoroutineTestInterceptor {
  override suspend fun intercept(testFunction: CoroutineTestFunction) {
    println("intercepting from SuspendingInterceptor")
    testFunction()
  }
}

class NonSuspendingInterceptor : TestInterceptor {
  override fun intercept(testFunction: TestFunction) {
    println("intercepting from NonSuspendingInterceptor")
    testFunction()
  }
}

class ExampleTest {
  @InterceptTest val nonSuspending = NonSuspendingInterceptor()
  @InterceptTest val suspending = SuspendingInterceptor()

  @Test fun suspendingTest() = runTest { println("running suspendingTest") }
  @Test fun nonSuspendingTest() = println("running nonSuspendingTest")
}

then have the SuspendingInterceptor pick up the suspendingTest, and NonSuspendingInterceptor pick up the nonSuspendingTest.

Originally posted by @jonapoul in #188

[JakeWharton]

I also have this need!

I have a class which is blocking for which most tests are also blocking. But for the occasional test I'm using runTest to get a scope into which I can launch something to occur in parallel.