Add CoreFoundation methods for getting current locale date format

[dbwiddis]

Maps methods needed to get the locale-specific date/time format. This is needed to parse the output of some command-line programs.

Motivation/sample code:

• Handle locale-specific formats on macOS system_profiler output oshi/oshi#2890

Another implementation:

• https://github.com/JetBrains/intellij-community/blob/e9f60b49d62a7d6be6f6b25929b293d48c7bf42d/platform/platform-api/src/com/intellij/util/text/DateFormatUtil.java#L333

Enum from the header file CFDateFormatter.h:

typedef CF_ENUM(CFIndex, CFDateFormatterStyle) {	// date and time format styles
    kCFDateFormatterNoStyle = 0,
    kCFDateFormatterShortStyle = 1,
    kCFDateFormatterMediumStyle = 2,
    kCFDateFormatterLongStyle = 3,
    kCFDateFormatterFullStyle = 4
};

[dbwiddis]

@matthiasblaesing any objection to me merging this?

[matthiasblaesing]

Looks sane to me.