* Added dependent BACnet stack headers into bacdef.h file.
* Changed bacdef.h and other stack includes in c/h files to have a common pattern.
* Moved bits.h, bytes.h, and bacnet_stack_exports.h under bacnet/basic/sys/ folder.
* Leverage (older) embedded unit tests into external unit tests build upon copy of Zephyr's ztest library and CMake.
* Expand top-level CMake build to run external unit tests.
* Expand Zephyr module extension to run external unit tests via west or sanitycheck.
Co-authored-by: Gregory Shue <gregory.shue@legrand.us>