Better detection of IsCollapsed state/changes on iPad Master View Controller

[PureWeen]

Description of Change

Fixed _masterVisible to be calculated instead of just depending on Disappear/Appear events. There are a bunch of edge cases where Disappear and Appear aren't called.

The main theme of this code change is to keep the cross platform IsPresented better in lined with the reality of the native code. The way events are thrown are also fairly different between iOS 12 and iOS 13

Platforms Affected

• iOS

Testing Procedure

Make sure to run all these tests on iOS 13 and iOS 12 as each platform runs fairly different

• run through Issue7556 and test as many combinations of rotating, pushing modal pages, rotating, and making sure Master button still works
• Test through Bugzilla34632Test and make sure it works as expected

PR Checklist

• Targets the correct branch
• Tests are passing (or failures are unrelated)