Rename semaphore and mutex shim functions according to FreeRTOS API

[agerasev]

Shim functions related to semaphores and mutexes affected:

• Changed function postfixes from *_mutex to *_semaphore (except mutex creation functions) to match FreeRTOS API names.
• Changed types from QueueHandle_t to SemaphoreHandle_t and from FreeRtosQueueHandle to FreeRtosSemaphoreHandle.
• Renamed arguments from mutex to semaphore.

[schteve]

Looks great! Glad to see a lot more alignment with the FreeRTOS API. Thanks!

As an idea for the future, one thing I noticed is that the existing code in the shim layer returns 0 or 1 as a proxy for a boolean. I wonder if there's opportunity to change those to bool. It seems based on this PR that bool is effectively the FFI type for itself, which is why there's nothing in ffi for it. I'm not 100% sure, but I'm having a hard time imagining a situation where this could cause any problems. Although, on second glance the 0 and 1 values are (at least sometimes) reversed - where 0 means success and 1 means failure. So we'd have to be careful to get the logic correct.

As a further idea for the future, it looks like these two functions are missing from the shim layer. We might want to add them someday. There are also FromISR variants for them.

• xSemaphoreGetMutexHolder()
• uxSemaphoreGetCount()