Convert SecurityManagerEventHandler into a pure interface.
Convert SecurityManagerEventHandler into a pure interface.

Convert most functions of SecurityManager into virtual pure functions.
Protect access to the get_event_handler function and remove function set_app_event_handler.

c1728p9/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,kjbracey-arm/mbed,betzw/mbed-os,betzw/mbed-os,betzw/mbed-os,mbedmicro/mbed,c1728p9/mbed-os,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,kjbracey-arm/mbed,andcor02/mbed-os,andcor02/mbed-os,mbedmicro/mbed,betzw/mbed-os,betzw/mbed-os,c1728p9/mbed-os,kjbracey-arm/mbed,kjbracey-arm/mbed,c1728p9/mbed-os,mbedmicro/mbed,andcor02/mbed-os,andcor02/mbed-os,c1728p9/mbed-os,betzw/mbed-os