Adding Office.onReady() (#25518)
Adding Office.onReady() (#25518)

Added declaration for Office.onReady() API.
dsebastien/DefinitelyTyped,dsebastien/DefinitelyTyped,borisyankov/DefinitelyTyped,rolandzwaga/DefinitelyTyped,AgentME/DefinitelyTyped,georgemarshall/DefinitelyTyped,georgemarshall/DefinitelyTyped,magny/DefinitelyTyped,AgentME/DefinitelyTyped,markogresak/DefinitelyTyped,rolandzwaga/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,georgemarshall/DefinitelyTyped,AgentME/DefinitelyTyped,one-pieces/DefinitelyTyped,magny/DefinitelyTyped,borisyankov/DefinitelyTyped,mcliment/DefinitelyTyped