[iOS] Disable compass fade when facing north

[chloekraw]

The default behavior on the Maps SDK fades out the compass when it's facing north. On @mapbox/maps-android, there is a boolean method MapboxMap.getUiSettings().setCompassFadeFacingNorth(false) to disable this fade. The same feature has been requested on iOS so that a developer can choose to always show the compass.

For other fade/animation customization options, we've faced a choice between whether to accept a boolean value or an integer, and the same question applies here. Accepting int is my preference -- it's more flexible because it supports the possibility of a future feature that enables the developer to customize the fade/animation duration, with 0 = disabled.

cc/ @mapbox/maps-ios

[friedbunny]

Duplicate of #9562.