Open App settings in iOS

[mvanbeusekom]

Added the openAppSettings API to iOS (note this PR adds to #4)

[dark-chocolate]

bool canOpenSettingsPage = await PermissionHandler().openAppSettings();
Doc says, it returns true if settings page can be opened and false otherwise. However in iOS, it opens settings page but still false is returned. So, please correct your docs.

Edit: By docs I meant your plugin docs, not the official docs of IOS or Android.

[mvanbeusekom]

@dark-chocolate, first the docs don't mention anything specific regarding the boolean being returned (which is definitely something we could/ need to approve on, pull-request are very welcome).

Second the idea of the boolean is not to indicate if the settings "can" be opened, but if it "was" opened successfully, meaning if true is returned the page has been opened and if false is returned the page could not be opened. Since you mentioned on iOS the a false is returned but the page is still opened I would say this is a bug and we need to look into that. To keep track of this bug I have create issue #52. Please feel free to add findings or other details there.

[dark-chocolate]

@mvanbeusekom Is there also a way to open Settings page in iOS (Settings here doesn't mean my own app settings, it means the general Settings app of iPhone)?