Read edits in a locale-independent manner

[Lysxia]

Issue mentioned on Zulip.

edits are currently read with text's readFile which seems to depend on the locale (like base). And by Murphy's law of locales it is going to be the wrong one for somebody. To make it more robust, we should just require UTF-8, by reading a bytestring and decoding it explicitly. And double check that the edits syntax handles \r for Windows.