Since FreeRTOS has real tasks and mutexes with support for priority bumping, actually always try and take a `CoreMutex` instead of seeing if someone else already has it and aborting immediately.
This fix helps ensure things like Serial output in a multi-task system won't get lost.
* Fix FreeRTOS CoreMutex shim to handle ISRs
Automatically check, when in FreeRTOS, if we're in an ISR and
if so call the correct mutex grab.
Thanks to @caveman99 for finding and proposing a solution!
Fixes#1441
* Fix the CoreMutex destructor, too
Fixes#1402
The global USB mutex is auto-shadowed with a FreeRTOS semaphore while in
FreeRTOS mode. Unfortunately, while the core was using the proper
FreeRTOS semaphore to lock access to the USB port, the actual FreeRTOS
USB task was using the naked Pico SDK mutex, leading to cases where it
could acquire the mutex even though some other FreeRTOS task actually
owned the shadowed mutex.
Properly lock the shadowed Semaphore, not mutex_t, in the FreeRTOS
USB periodic task.
