HardwareTimer: rework internal mapping of arduino API with HAL/LL API

Main rework:
* HAL_TIM_Base_Init() is now called only once at object creation
* HAL_TIM_xxx_ConfigChannel is now done in setMode()
* HAL_TIM_xxx_Start is done in resumeChannel()
* use LL when possible
* Configuration are directly made through hardware register access (xhen possible),
  then remove useless attribut
* Add new API to pause only one channel: pauseChannel(uint32_t channel)
  fixes stm32duino#763
* integration of PR stm32duino#767 Flexible interrupts handling

Author: ABOSTM