fix thread renaming

[kripergvg]

Thread renaming is quite common operation. In current implementation thread is distinguished by name and if it's renamed it's not tracked properly.
I suggest using ManagedThreadId instead. If you run the new "TestThreadRenamed" test on old implementation you can reproduce the problem.

[pdeligia]

Thanks for your PR @kripergvg, however sadly AFAIK ManagedThreadId can break the runtime because although the id is unique, it can be reused by subsequent threads which makes it not a good choice for a dictionary key in this case. That is the original reason we avoided using it, and instead opted for thread naming -- although I agree with what you say its not ideal, and does not work well with cases where someone has already named threads. Our focus until recently has been higher-level C# code that uses tasks (from TPL) rather than lower-level threads, so this renaming situation was uncommon. We need to figure out a better solution moving forward to better support low-level threading scenarios.

[kripergvg]

@pdeligia I see. What about using the thread instance directly as a key in dictionary?