[BottomNav][iOS] Changing tabs programatically messes up styles

[PeterStaev]

Environment
Provide version numbers for the following components (information can be retrieved by running tns info in your project folder or by inspecting the package.json of the project):

• CLI: 6.0.0
• Cross-platform modules: 6.0.0
• Android Runtime: 6.0.0
• iOS Runtime: 6.0.0
• Plugin(s):

Describe the bug
When you change the selectedIndex programatically the tab actually changes but the styles are not applied, so visually the old tab remains selected and the new one looks like unselected. Works as expected on android.

To Reproduce
https://play.nativescript.org/?template=play-tsc&id=ill2KK
tap on button in the action bar

Expected behavior
Styles to be applied correctly.

Sample project

Additional context

Related to #6967

[ycherniavskyi]

The same happens when Label and Image elements used inside TabStripItem - https://play.nativescript.org/?template=play-tsc&id=kI4O0n&v=2

And unfortunately, it is reproduced under the last NS 6.2 release.