This introduces a new testing helper to package tracing which we can use
to make sure that context.Context values are able to reach all the way
from a test caller to some specific function elsewhere in the system.
We then use that helper in package tofu to test whether context values are
able to reach calls to providers, which tend to be the deepest place that
package tofu is responsible for routing them to.
As of this test the providers.Interface.Configure method does not seem to
receive values, so that is currently commented out in this test and we'll
deal with that properly in a subsequent commit.
Signed-off-by: Martin Atkins <mart@degeneration.co.uk>
