[Enhancement] Renderer need some override method for native platform like android lifetime manage

[jingliancui]

Summary

Something 3rd party library like the Amap (a map product in china),It include the navi view feature with lifetime managed.After finished the binding work.It can be use in the Xamarin.Forms project using the renderer feature,or use it in the Xamarin.Android project.
In the Xamarin.Android, the navi view's lifetime managed can be invoke by the OnResume(),OnPause() etc... which are override method in the Activity.
But the Xamarin.Forms' side,It's only has one MainActivity to manage these lifetime methods,then on renderer side,I must get the native control from the member of the MainActivity.

Sample code here:

https://github.com/jingliancui/XamarinFormsAMapSDKSample/blob/master/Android/Newest/SampleApp/SampleApp/SampleApp.Android/Renderers/AMapNaviViewRenderer.cs#L35

https://github.com/jingliancui/XamarinFormsAMapSDKSample/blob/master/Android/Newest/SampleApp/SampleApp/SampleApp.Android/MainActivity.cs#L120

API Changes

Add OnResume(),OnPause(),OnDestroy() ... etc which are lifetime managed methods to Renderer base class .

Intended Use Case

Add OnResume(),OnPause(),OnDestroy() ... etc which are lifetime managed methods to Renderer base class .

[davidortinau]

How might this work with #28 Slim Renderer Architecture @Clancey @PureWeen?

[PureWeen]

Not sure off hand but this is a good idea. It'll probable be very similar to how the current mappers are setup and we can add some lifecycle actions or keys to the mapper you can opt into.

The tricky thing here might be performance. We don't want to just activate watching all life cycle events out of the box they should get attached once we know the user wants to opt in