[TIMOB-23857] iOS: Expose more Pasteboard Item's APIs

With the expansion of Pasteboard support in iOS 10, it would be helpful to have more of the APIs for Pasteboard manipulation exposed. Ideally, we would support all listed in https://developer.apple.com/reference/uikit/uipasteboard Previously we mainly supported Pasteboards with single items. Many of these APIs would add support for using multiple Pasteboard items. Proposed APIs to expose: var *types*: \[String\] - added in iOS 10 func *contains*(pasteboardTypes: \[String\]) func *value*(forPasteboardType: String) func *setValue*(Any, forPasteboardType: String) var *numberOfItems*: Int func *contains*(pasteboardTypes: \[String\], inItemSet: IndexSet?) func *data*(forPasteboardType: String, inItemSet: IndexSet?) func *values*(forPasteboardType: String, inItemSet: IndexSet?) func *addItems*(\[\[String : Any\]\])