[application] Clarify that getIosPushNotificationServiceEnvironmentAsync returns null on the simulator

[tsapeta]

Why

The docs say that Application.getIosPushNotificationServiceEnvironmentAsync returns "development" or "production". However, since the simulator doesn't support push notifications, it returns undefined in that case.

How

• Explicitly return null instead of undefined on the simulator (and backported this change to SDK46)
• Clarify in the docs that it can return null
• Fixed test-suite test that expected a string
• Regenerated API docs for this package (also for SDK46)

Test Plan

Now the updated test passes on the simulator