feat(ios): opt-out new tab bar under iPadOS 18+

[hbugdoll]

Fixes #14123.

Introduction:
A new floating tab bar was introduced in iPadOS 18 which is displayed without tab icons and at the top of the screen.
This breaked many custom UI and CD/CI, see also issue above or recently in Slack.

Description:

• added property forceBottomPosition to TagGroup for iPad
  • forcing the tab bar to be displayed in the old style
  • works also under iPadOS 26 – is indeed a “floating” tab bar, but with icons and at the bottom of the screen (as on iPhone)
• updated apidoc

Screenshots:

iPadOS 18:

forceBottomPosition = false (default)	forceBottomPosition = true

iPadOS 26:

forceBottomPosition = false (default)	forceBottomPosition = true

Usage:

const tabGroup = Ti.UI.createTabGroup({
    tabs: [tab1, tab2],
    forceBottomPosition: true
});