Implement "Screen size to switch to mobile header" to Adv Header block#35

The classic Kadence theme header has a “Screen size to switch to mobile header” setting, but the Advanced Header block doesn’t; requesting the same breakpoint control be added there to prevent nav items wrapping to a second line on tablets. (Migrated from featureOS: https://feedback.kadencewp.com/p/implement-screen-size-to-switch-to-mobile-header-to-adv-header-block)