Removed Unneccessary !'s from public variables in NSDateFormatter

[natemann]

Each public variable was cast as a forced unwrap. I do not believe this is necessary as each variable has a getter & setter.

I do have a question with

internal var _dateFormat: String?
    public var dateFormat: String {
        get {
            if let format = _dateFormat {
                return format
            } else {
                if let obj = __cfObject {
                    return CFDateFormatterGetFormat(obj)._swiftObject
                } else {
                    return ""
                }
            }
        }
        set {
            _reset()
            _dateFormat = newValue
        }
    }

I changed the return to String, from the original String?. If the desired return is String?, I believe the get should be

get {
            if let format = _dateFormat {
                return format
            } else {
                if let obj = __cfObject {
                    return CFDateFormatterGetFormat(obj)._swiftObject
                } else {
                    return nil
                }
            }
        }

[parkera]

The reason that these are ! is because they are null_resettable in Objective-C. That is, it's valid to set them to nil but you will never get nil back. We should preserve that contract in Swift as well.

[parkera]

Here is the API in Objective-C:

@property (null_resettable, copy) NSString *dateFormat;
@property NSDateFormatterStyle dateStyle;
@property NSDateFormatterStyle timeStyle;
@property (null_resettable, copy) NSLocale *locale;
@property BOOL generatesCalendarDates;
@property NSDateFormatterBehavior formatterBehavior;
@property (null_resettable, copy) NSTimeZone *timeZone;
@property (null_resettable, copy) NSCalendar *calendar;
@property (getter=isLenient) BOOL lenient;
@property (nullable, copy) NSDate *twoDigitStartDate;
@property (nullable, copy) NSDate *defaultDate;
@property (null_resettable, copy) NSArray<NSString *> *eraSymbols;
@property (null_resettable, copy) NSArray<NSString *> *monthSymbols;
@property (null_resettable, copy) NSArray<NSString *> *shortMonthSymbols;
@property (null_resettable, copy) NSArray<NSString *> *weekdaySymbols;
@property (null_resettable, copy) NSArray<NSString *> *shortWeekdaySymbols;
@property (null_resettable, copy) NSString *AMSymbol;
@property (null_resettable, copy) NSString *PMSymbol;
@property (null_resettable, copy) NSArray<NSString *> *longEraSymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *veryShortMonthSymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *standaloneMonthSymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *shortStandaloneMonthSymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *veryShortStandaloneMonthSymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *veryShortWeekdaySymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *standaloneWeekdaySymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *shortStandaloneWeekdaySymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *veryShortStandaloneWeekdaySymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *quarterSymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *shortQuarterSymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *standaloneQuarterSymbols NS_AVAILABLE(10_5, 2_0);
@property (null_resettable, copy) NSArray<NSString *> *shortStandaloneQuarterSymbols NS_AVAILABLE(10_5, 2_0);
@property (nullable, copy) NSDate *gregorianStartDate NS_AVAILABLE(10_5, 2_0);
@property BOOL doesRelativeDateFormatting NS_AVAILABLE(10_6, 4_0);