Added support for reduced accuracy detection on iOS 14 - #1739

Description of Change

iOS 14 added the ability for users to grant location permission with reduced accuracy.
In such cases the requested accuracy is ignored and the coarse location is returned.

This PR adds:

• A property indicating if the retrieved location has reduced accuracy (if true, the accuracy was intentionally reduced by the user through permission settings)
• A property to ask the user for temporary full accuracy authorization in the location request

Platform notes:

• The ReducedAccuracy property always returns false on non-iOS platforms
• As described in the Apple documentation; on iOS the temporary full accuracy request requires a purpose description to be added to the NSLocationTemporaryUsageDescriptionDictionary in the app's plist file. The key XamarinEssentialsFullAccuracyUsageDescription was used for this purpose.

Bugs Fixed

• Fixes issue [iOS] Add support for detecting whether the granted location is Precise #1523

API Changes

Added:

• bool Location.ReducedAccuracy { get; set; }
• bool GeolocationRequest.RequestFullAccuracy { get; set; }

PR Checklist

• Has tests (if omitted, state reason in description)
• Has samples (if omitted, state reason in description)
• Rebased on top of main at time of PR
• Changes adhere to coding standard
• Updated documentation (see walkthrough)