Core::PauseAndLock requires all calls to it to be balanced, like this:
const bool was_unpaused = Core::PauseAndLock(true);
// do stuff on the CPU thread
Core::PauseAndLock(false, was_unpaused);
Aside from being a bit cumbersome, it turns out all callers really
don't need to know about was_unpaused at all. They just need to do
something on the CPU thread safely, including locking/unlocking.
So this commit replaces Core::PauseAndLock with a function that
makes both the purpose and the scope of what is being run on the
CPU thread visually clear. This makes it harder to accidentally run
something on the wrong thread, or forget the second call to
PauseAndLock to unpause, or forget that it needs to be passed
was_unpaused at the end.
We also don't need comments to indicate code X is being run on the
CPU thread anymore, as the function name makes it obvious.
