Prevent Displaying events from being called when a shape is cached

[sebastienros]

c.f. #16677

Ideally the lambda passed to a driver in the initializing argument should not be called when caching is kicking in. But then we need a new event such that caching can happen BEFORE "displaying", which we don't have. And maybe two more events: one to initialize, such that "displaying" events know that the object has the properties it requires, and one before that such that "caching" can prevent initialize to happen.

Another options, which would not require new events or breaking changes is that after the IShapeDisplayEvents.DisplayingAsync invocations, we check if the ChildContent has been set and skip other DisplayingAsync event (called by the drivers and shape descriptors). Processing would then be useless.

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