TIMOB-13901: adding an iOS Label method to calculate the height

It turns out that for iOS we need to calculate ListView item heights. The issue is usually caused by wrapped labels, thus we need a method to calculate label heights, given a known width.
`var calculatedHeight = myLabel.heightFromWidth(100);` for example will provide the label's height, constrained to a width of 100, assuming word wrap behavior and accounting for the label's font.