* 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

Add missing values that are present in pal::AttErrorResponse.
This allows applications to use correct ATT error codes.

Update parameters passed to onDataSent, onUpdatesEnabled/Disabled, and onConfirmationReceived callbacks.

Deprecate single-callback-registering functions for event handling in lieu of the new EventHandler-based API.

Introduce new GattServer::EventHandler callback functions to replace the deprecated versions.

The ChainableGapEventHandler enables chaining together Gap::EventHandlers so separate parts of an application can be notified of Gap events as needed. The application can register multiple Gap::EventHandler objects to one ChainableGapEventHandler and then set the global Gap::EventHandler to the ChainableGapEventHandler. All registered EventHandlers will then be called when a Gap Event occurs.

Common functionality has been split off into a generic ChainableEventHandler for use by other EventHandler implementations. The ChainableEventHandler is essentially singly-linked list that propagates callbacks to all objects in the list.

The ChainableGattServerEventHandler enables chaining together GattServer::EventHandlers. An application can register separate event handlers (eg: for different services that need to handle GattServer events) and then set the global GattServer::setEventHandler to the instance of ChainableGattServerEventHandler with all registered GattServer::EventHandlers.

Move private headers GattServerEvents.h, GapEvents,h and GapType.h in relevant part of the source tree.