[TIMOB-20129] Windows: API for Xaml Inline text element

Background

Titanium API has Ti.UI.AttributedString API to style text element in Ti.UI.Label etc, but it's basically designed based on [NSAttributedString](https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSAttributedString_Class/) in iOS. Since Windows has its own [unique API for text-styling](https://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.documents.inline.aspx), we might want to define Windows-specific API for text styling to leverage them. - [Windows::UI::Xaml::Documents.Inline](https://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.documents.inline.aspx) - [Windows::UI::Xaml::Documents.Run](https://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.documents.run.aspx) - [Windows::UI::Xaml::Documents.Span](https://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.documents.span.aspx) - [Windows::UI::Xaml::Documents.Underline](https://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.documents.underline.aspx) - [Windows::UI::Xaml::Documents.Hyperlink](https://msdn.microsoft.com/en-us/library/windows/apps/windows.ui.xaml.documents.hyperlink.aspx)