mbed-ce@master + fixes + gcc 11 support (#135) ...

* Fix rtos::Mutex stub, add trylock() method

* LowPowerTicker - Add ::attach(...) method + call callback

* mbed_power_management - rename sleep --> mbed_sleep to avoid conflicts

Fixes conflicts w/ unistd.h and boost::ut

* GCC 11/C++ 20 - Remove deprecated type_traits

* GCC 11/C++ 20 - Remove redundant templating of methods

* Warning - pragma ignore invalid-noreturn for unit tests

* Fix astyle errors

* Fix missing mbed_sleep() calls

Fix MBED_ERROR call in init_os_timer

Update platform/source/mbed_os_timer.cpp ...

fix the typo

Co-authored-by: Lingkai Dong <lingkai.dong@arm.com>

platform: move internal headers to internal/ ...

They belong to internal folder to follow our guideline, not in source as they were.

platform: remove platform/ prefix for source ...

If we take platform as a component, platform/source would be outside of this component.
I removed the prefix as these are implementation specific (they are located in source folder,
not in include as the others).

OS timer uses LPTICKER by default, then USTICKER ...

This PR makes the bare-metal mode work automatically
regardless of the tickless-from-us-ticker setting
- in non RTOS mode
- and in RTOS tickless mode

Correct core RTOS sleep routine timing ...

Chrono conversions inadvertantly changed the core timed sleep routine
used by the RTOS idle to use `OsTimer::update_and_get_tick()` instead of
`OsTimer::get_tick()`.

Correct this, and expand/clarify documentation and naming to try to
prevent recurrence.

Another minor fix observed while inspecting code - `OsClock` can't just
use `milliseconds`, it should match the period of `OsTimer`, which
theoretically can be different.

Add Chrono support to Kernel and SysTimer

Fix thread_sleep_for zero

Move source files and add Doxygen labels