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What is the current behavior?

Views and view trees are destroyed when removed from the view tree.

What is the new behavior?

Views can be marked as reusable and will not be destroyed when removed from view tree. Removing these nodes require the developer to do:

view.destroyNode();
// which calls
view.reusable = false;
view._tearDownUI();

For implementation details on how frameworks should deal with it, see my work in nativescript-angular: https://github.com/edusperoni/nativescript-angular/tree/reusable-views

Implements #7469.
Rewrite of #8184

To be defined:

What happens when a reusable view with children gets removed? The current implementation does not call _tearDownUI on children, but we should still suspendNativeUpdates down the chain (this._suspendNativeUpdates(SuspendType.UISetup);).

Maybe we should we create a new SuspendType (Detached)? Maybe this isn't even needed as the view should be unloaded by _removeViewCore which eventually calls this._suspendNativeUpdates(SuspendType.Loaded); on all children.

Possible refactoring needed (not directly related to this PR)

The current logic of _resumeNativeUpdates will call initNativeView. In most places I checked, initNativeView creates delegates that are only removed in disposeNativeView. This behavior is probably already an issue on loading/unloading views (like navigation) because of this._resumeNativeUpdates(SuspendType.Loaded);, meaning initNativeView is called multiple times during the application lifecycle, but the delegates are only cleaned up once.

During my tests with WebView, calling initNativeView did not result in a performance impact