Implement UITableView

[ephemer]

Motivation

UITableView is one of the fundamental classes made available to display data in UIKit. It's not used by flowkey's app, so we have no implemented it yet. Like CGContext, UITableView has been implemented in https://github.com/PureSwift/Cacao, and @colemancda has indicated that we'd be fine to use his existing implementation.

So this work would involve adapting the code @colemancda has made to our UIKit internals, and adding tests (preferably also in iOSTestTarget).

[colemancda]

@ephemer Any update on this? I am curious to see if it will run more performant on your UIKit implementation. Basically my SDL event run loop is not optimized on Linux and lags when scrolling.