Improve `objc2::foundation`

[madsmtm]

Collection of ideas to improve objc2-foundation

• [ ] Add more iterator methods to INSArray and INSMutableArray (see also https://github.com/madsmtm/objc2/issues/29#issuecomment-913185651)
• [ ] Safety of NSArray::objects_in_range (out of bounds?)
• [x] ~Add INSString::to_string to avoid having to use autoreleasepool~ This is already available via. Display
• [x] Figure out how NSNumber vs. NSValue should work - done in #226
• [ ] Lifetime parameter on NSString/NSData and subclasses, so that initWithBytesNoCopy can work?
• [ ] NSData index with ranges / SliceIndex?
• [x] NSSize validity: https://github.com/madsmtm/objc2/pull/260
• [ ] Iteration improvements, see also https://clang.llvm.org/docs/AutomaticReferenceCounting.html#fast-enumeration-iteration-variables
• [ ] ...

Add these classes/structs that are used by winit:

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

An furthermore these that are available in cocoa-foundation:

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

And a few that makes sense to do:

• [x] NSSet/NSMutableSet - https://github.com/madsmtm/objc2/pull/245
• [x] NSMutableDictionary - https://github.com/madsmtm/objc2/pull/249