Dissallow non-standard event properties as extendedProps to improve type-checking of standard event properties

[its-dibo]

Reduced Test Case

.

Do you understand that if a reduced test case is not provided, we will intentionally delay triaging of your ticket?

• I understand

Which connector are you using (React/Angular/etc)?

Angular

Bug Description

the docs says that you can add "any other properties" that are moved into extendedProps{} object of events properties.

however, this causes a couple of issues

• that the type-checking can not detect typos for existing props
• properties in extendedProps can be overridden by those props (or maybe the vice versa) which causes unexpected result

let calenderOptions: CalenderOptions = {
 events: {
   //<-- typo: should be 'title', but the type-checking accepted it as it is an extra prop
   tilte: "event title",
   extendedProp:{
    //<--- this may be unintentionally overridden
     isActive: true
  },
isActive: false
}
}