[sweet][kotlin] Add basic view's callbacks support

[lukmccall]

Why

Adds a very primitive view callbacks support.

How

• Extends a ViewManager DSL.
• Creates a property delegate that handles callbacks.

Note

• currently, we only support bundle as an event payload
• you have to call invoke method on the Callback instance - it will be changed in the future

Test Plan

• bare-expo ✅

How to create a callback

// module definition
ViewManager {
	// ...
	callbacks("onChange")
}

// view
class MyView : View {
	val onChange by callback<Bundle>()

	fun invokeOnChange(event: Bundle) {
		onChange.invoke(event)
	}
}

[lukmccall]

Suggested change

	fun callbacks(vararg callbacks: String) {
	fun events(vararg callbacks: String) {

@tsapeta, I saw that you called it events on iOS. Should I rename it?

[tsapeta]

Yeah, I think it makes sense to call them events, as React Native does. I also just reused the component that we have in the module scope 😉
Imho the name and type "Callback" can also be used in the future for function arguments that are functions on the JS side 🤔

[bbarthec]

Awesome work 👏
Can't wait for the final result! 😁
Before merging make sure the naming is consistent with iOS platform 👀

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