Standardize NSException names

[1ec5]

Most of the NSExceptions we raise in the iOS and macOS SDKs are named with ad-hoc names such as “Value not handled”. Instead, we should either use one of the predefined exception names or define a string constant such as “MGLIdentifierCollisionException” in MGLTypes.h for use with these exceptions. This way, test code can more easily check for the exception with XCTAssertThrowsSpecificNamed(), and we could start adding notes about exception conditions in our method documentation.

/cc @incanus @frederoni

[fabian-guerra]

Predefined exception names link update.