Implemented text selection!

And at the end I show you can Ctrl+A.
Things left would be bidirectional selection rects, clipboard, and... multiline text editing.
I gave up on multiline because I just can't do it with parley. Probably a skill issue or I missed something. So that's gonna wait til I make text layouting myself.
And I'm gonna do clipboard before the bidirectional selection rects because I need to paste some arabic.