fix(iOS): extraLight blur not working

[maksg]

Description

Blur style UIBlurEffectStyleExtraLight equals 0 so using it in if (config.blurEffect) makes it that the code for applying backgroundEffect doesn't execute.

With this fix the navigation bar can no longer be fully transparent because blur effect is always set as extraLight by default. So it's up for a discussion if it should stay that way or if we should make this value optional.

Fixes #2320.

Test code and steps to reproduce

Added Test2320 to tests.

Checklist

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

[kkafar]

Good catch, but we rather don't want to go this way.
Let's add a option unspecified, but only for internal API usage (do not include this option in public API), and when blurEffect has undefined / nullish value, in bottom-level Screen component (just in the wrapper for NativeScreenComponent) let's make use of this Unspecified / Undefined enum variant and pass it to native side. Then in headerConfig check for variant value.

Does that sound right?

[maksg]

@kkafar I added custom enum value UIBlurEffectStyleUndefined so it looks pretty clean.
Let me know if this approach is good enough or I should change it.