StopUnderDriveMode_Measure() function

This function configures the system to enter Under-Drive stop mode with RTC clocked by LSE or LSI for current consumption measurement purpose. STOP Mode with RTC clocked by LSE/LSI ===================================== - RTC Clocked by LSE or LSI - Regulator in LP mode - Under drive feature enabled - HSI, HSE OFF and LSI OFF if not used as RTC Clock source - No IWDG - FLASH in deep power down mode - Automatic Wakeup using RTC clocked by LSE/LSI (~20s)