Word-wrap and general text performance

[tienery]

Currently, the TextBox control is not particularly performant when dealing with large amounts of text. This is especially true due to the way "word-wrapping" is handled.

This issue should resolve and implement the following:

• Implement a way to deal with word-wrapping on a line-by-line basis, rather than character by character.
• Only perform word-wrapping on affected lines rather than re-format the entire text box.
• Multi-thread/use async tasks to perform formatting on large amounts of text greater than a specific amount of characters.

The project could also do with a text engine overhaul, with text rendering done on a separate buffer, but one performance problem at a time, I think!