Make Animated Value persist its value after reattaching

[osdnk]

When value gets detached from all component it can be still kept in memory and attached to some other component at later time. But because we don't know when JS reference is dropped we need to delete native counterpart of the value when it gets detached. This has led to a situation in which the value was reinstantiated on the native site. In that case if the value has changed we expect it to persist that changes when it gets attached again. This wasn't happening and each time the value was instantiated we'd always use the initial value.

With this change we are solving that issue by querying the value right before we detach the native node and then we use that value to update config such that next time when it gets instantiated it uses updated value instead of the initial one.

[osdnk]

related: #85

[osdnk]

Make this destruction in order not to fleeze value field

[kmagiera]

This looks good but I think it would be easier to use callback to get the value instead of introducing new event type. That is have a method:

ReanimatedModule.getValue(this.__nodeID, v => {
   this.__nodeConfig.value = v;
});

[osdnk]

@kmagiera
Now I am not convinced at all about this change. I'm afraid of blinking with some edge cases like this one which @ericvicenti has shown

[ckknight]

@kmagiera Why use a callback instead of returning a promise?

[kmagiera]

@osdnk looks like the blinking problem wasn't related to the problem

@ckknight we can also use promise instead of callback, what I wanted to get rid is that special type of event that we expect to be sent when we call a method. Much cleaner pattern would be to call getValue method and expect it to return its value asynchronously (e.g. via callback or a promise) instead of complicating its contract and expecting special even to be returned.

[kmagiera]

Looks good, can you think of an example we can add to test if this continue to work in the future

[kmagiera]

import cleanup