Issue #3206643 by fjgarlin, Lal_, AJV009, quietone, benjifisher, mohit_aghera,...

Issue #3206643 by fjgarlin, Lal_, AJV009, quietone, benjifisher, mohit_aghera, larowlan, VladimirAus, mherchel, xjm, alexpott, Rishabh Vishwakarma, ckrina, rkoller, Gábor Hojtsy, smustgrave, AkshayAdhav, hestenet, irinaz, AaronMcHale, andrewmacpherson, longwave, catch, shaal, nod_, drumm: Project messaging channel in core (as experimental)