Deprecating performance counters in favor of task hooks

[jhnphm]

The performance counters don't account for every task in the system and are somewhat lacking in capability (i.e. isn't able to log which core something is scheduled on).

Instead, for VxWorks at least, there's taskSwitchHookAdd. For Linux, there's perf. FreeRTOS has vTaskSwitchContextHook, and I think on RTEMS rtems_task_switch_extension can be used.

For past projects I've written scripts to convert context switch logs to .vcd files for viewing in GTKWave.

The existing perfmon infrastructure does have the advantage that it can log arbitrary portions of task execution rather than just scheduling in/out, so it should probably be kept for that, but the explicit task enter/exit log entries could be deprecated.

[jhnphm]

Could probably have the task hook scripts output to the same log as the existing perfmon infrastructure as well.