This allows high-level library classes to implement enhanced simulation
support even if no low-level corresponding simulation library exists, and
avoids the need for bit-banging complex interfaces like SPI or CAN.
std::scoped_lock was introduced in C++17 and is strictly better than
std::lock_guard as it supports locking any number of mutexes safely.
It's also easier to use than std::lock for locking multiple mutexes at
once.
The 2019 FPGA image switched the output of auto SPI from plain bytes to a
sequence of 32-bit words (timestamp, then words with the byte values in the
least significant byte of each word).
In addition to changing the HAL and simulators to reflect this, add piecewise
integration support to wpilibc/wpilibj SPI to take advantage of the timestamps
and use it in the ADXRS450 gyro.
This makes callback registration completely thread safe.
This patch also uses templates and macros to dramatically reduce the amount of
manual boilerplate.
The old headers were moved into folders because doing so avoids polluting
the system include directories.
Folder names were also normalized to lowercase.
