[TIMOB-9974] TiAPI: Need the ability to adjust the line height / leading of text components

For text components like UILabel we need the ability to adjust the line height / leading / vertical spacing. This is an important typographical control. An example of controlling line height: https://img.skitch.com/20120717-cfr4cp64hyk59xk21rtpkjx2iy.png - I'm talking about the space between the lines of this text label. With brief research it doesn't look like it's possible out of the box with a UILabel in iOS and what most people have done is subclass the UILabel class to allow for this control.