This commit introduce three new `til` features:
* "til/latch.h": A std::latch clone, until we're on C++20.
* "til/mutex.h": A safe mutex wrapper, which only allows you access to the protected data after locking it. No more forgetting to lock mutexes!
* "til/throttled_func.h": Function invocation throttling used to be available as the `ThrottledFunc` class already. But this class is vastly more efficient and doesn't rely on any WinRT types.
This PR also adds a `til::ends_with` string helper which is `til::starts_with` counterpart.
## Validation Steps Performed
* Scrollbar throttling still works as it used to ✔️
* No performance regressions when printing big.txt ✔️Closes#10393
0d9a357373