When it comes to startup profiling, it is very helpful to look at platform channels. `debugProfilePlatformChannels` today only works in debug and profile mode. Unfortunately, using profile mode is less accurate for startup profiling, because of the service isolate introducing additional overhead.

This PR allows this toggle to work in release mode. Note that there are two parts to `debugProfilePlatformChannels`:

- Adding timeline events
- Logging statistics about platform channels

I also considered adding a separate toggle to limit the scope of this change to the former, but that seems like complexity that we might not need at this time.

Towards #102189