fix(iOS): do not force API user to set activityState

[kkafar]

Description

We did not set default value of activityState on iOS. It was set to 0 by default int initializer.

In Screen component native spec we set it to -1, however this had no impact, because the value setter
setActivityStateOrNil: filtered out the -1 value.

TODO:

1. Verify that change in default value do not break any other navigator!

^ Looks like this will work, because navigators such as bottom tabs always set the activity state explicitly.

This is a problem, because now, after adding preload support #2389 we filter out screens with activityState == 0 in native stack.
Therefore, we now unintentionally force our API user to always set desired activityState.

Fixes #2405

Changes

Set activityState to -1 by default on native side.

Test code and steps to reproduce

Just render screen inside native-stack w/o activityState set. It won't be shown.

Checklist

• Included code example that can be used to test this change
• Ensured that CI passes