Out-of-line LowPowerTimeout etc, lock ...

To match Timer etc, make LowPowerTimer et al out-of-line.

Correct LowPowerTimeout to not lock deep sleep.

Add Chrono support to Ticker et al

Turn NULLs into nullptr ...

Avoids overload problems with Callback(nullptr) versus Callback(fnptr).

Remove deprecated FunctionPointer class

Fix Coverity issues ...

Issues fixed are related to:
* Non-static class member initialization in constructors
* Unused function return value
* Always false statements

Drivers/Events/RTOS Public and internal APIs cleanup (#10955) ...

Separate drivers, events, and rtos internal APIs from public APIs.

* Move source files to source subdirs
* Move internal headers to internal subdirs
* Add Doxygen comments for documenting internal and public APIs
* Remove source code from header files in order to remove include pre-processor directives
that included header files not directly used by said header files
* Explicitly include header files instead of implicit inclusions via third-party header files.

Release Notes

This will break user code that was using an internal API as the internal header files have been moved.
This will only break if the user was including the header file using a namespace (i.e #include "foo/bar.h" instead of #include "bar.h"