Fixed Unity not receiving lifecycle events from iOS

[jakeobrien]

Description

There are some casting bugs preventing iOS lifecycle events (didBecomeActive, wilEnterForeground, etc) from reaching unity. This causes two issues:

• OnApplicationPaused() callbacks don't fire in unity
• When the app is backgrounded, Unity does not pause, causing high cpu/battery usage while backgrounded

This patch fixes these casting bugs.

Specifically:

• line 173 fixes an attempted cast of the .appController() method itself to the object the method returns. Since the method isn't actually called, nothing is returned and the casting fails.
• lines 202-208 fix an attempted cast of NSNotification.Name (an enum) to a String. This cast fails and so the code path wiring up the observer is skipped.

Type of Change

• ✨ New feature (non-breaking change which adds functionality)
• 🛠️ Bug fix (non-breaking change which fixes an issue)
• ❌ Breaking change (fix or feature that would cause existing functionality to change)
• 🧹 Code refactor
• ✅ Build configuration change
• 📝 Documentation
• 🗑️ Chore