Task snapshot API were never intended to be called from user code. This commit
makes task snapshot a private API thus moves `#include "freertos/task_snapshot.h"`
to `#include "esp_private/freertos_debug.h"`.
Task snapshot related Kconfig options have also been hidden.
Note: Added 'freertos_common' mapping to ldgen mapping execptions lists due to
inlining of 'freertos_debug.h' functions.
