fix(iOS, Tabs): update tab bar item only when necessary

[kligarski]

Description

Limits changing tab bar item instances (PR introducing this) to only necessary cases (changing systemItem). Unnecessary updates caused a bug when changing e.g. only badgeValue.

before	after
before.mov	after.mov

Fixes #3273.

Changes

• separate creating new UITabBarItem instance and updating tab bar item related props
• create new UITabBarItem instance only on systemItem change
• restore default system item's icon by extracting it from new UITabBarSystemItem instance instead of changing the entire UITabBarItem

Test code and steps to reproduce

Run TestBottomTabs. Change badgeValue on selected tab. You can also check test cases from #3164.

Checklist

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