fix(ios): exit event not fired on swipe down

[jcesarmobile]

Platforms affected

ios

Motivation and Context

fixes #718

Description

if presenting IAB on not full screen styles, when the user closes IAB using swipe down gesture instead of the close button the exit event is not fired

exit event is fired on viewDidDisappear, but only if isExiting is set to true, this PR uses the UIAdaptivePresentationControllerDelegate to detect when the modal is being dismissed and set isExiting to true so exit fires on viewDidDisappear

Testing

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[erisu]

LGTM

[kartiksolanki]

Hi,
I tried above changes in my project and while the modal dismiss exit event is fired, I am now facing with UI presentation. So my modal has a close button and, when i do the presentation style to pagesheet (which appears like ios13 modal), the top navigation bar of the modal becomes transparent. I am attaching the image below for your reference.

[kartiksolanki]

Any idea what is going wrong in here? As you can see from the above screenshot, my modal top navigation appears as transparent on top of my default page calling the in app browser.