swift

09779202 - [Concurrency] Add tracing for major operations in the concurrency runtime.

[Concurrency] Add tracing for major operations in the concurrency runtime. Each trace point is declared as a function in the new `Tracing.h` header. These functions are called from the appropriate places in the concurrency runtime. On Darwin, an implementation of these functions is provided which uses the `os/signpost.h` API to emit signpost events/intervals. When the signpost API is not available, no-op stub implementations are provided. Implementations for other OSes can be provided by providing implementations of the trace functions for that OS. rdar://81858487