Improve objc2::foundation

[madsmtm]

Collection of ideas to improve objc2-foundation

• Add more iterator methods to INSArray and INSMutableArray Moved to Proper iteration over Foundation types #304
• Safety of NSArray::objects_in_range (out of bounds?)
• Add INSString::to_string to avoid having to use autoreleasepool This is already available via. Display
• Figure out how NSNumber vs. NSValue should work - done in Improve NSValue and add NSNumber #226
• Lifetime parameter on NSString/NSData and subclasses, so that initWithBytesNoCopy can work?
  • I won't be doing this, the complexity penalty to the normal use-cases is just too high. If desired one can always struct MyNSString<'a>(NSString, PhantomData<&'a >)
• NSData index with ranges / SliceIndex?
• NSSize validity: Rework Foundation geometry types #260
• Iteration improvements, moved to Proper iteration over Foundation types #304

Add these classes/structs that are used by winit:

• NSThread
• NSString
• NSAttributedString
• NSAttributedMutableString
• NSArray
• NSProcessInfo
• NSDictionary
• NSData
• NSFastEnumeration
• NSNotificationCenter
• NSTimeInterval
• NSPoint
• NSRect
• NSSize
• NSRange

An furthermore these that are available in cocoa-foundation:

• NSOperatingSystemVersion
• More NSProcessInfo methods
• NSEnumerationOptions?
• NSDate
• NSRunLoop
• NSURL
• NSBundle
• NSData base64 functionality?
• NSUserDefaults

And a few that makes sense to do:

• NSSet/NSMutableSet - Add NSSet and NSMutableSet #245
• NSMutableDictionary - Add NSMutableDictionary #249

And many more, since #264

[madsmtm]

Fixed by #308