Remove use `flex-direction: column-reverse;` for message container.

[creesch]

This line specifically: https://github.com/creesch/minecraft-web-chat/blob/main/src/client/resources/web/css/main.css#L237

I used it because it makes things a bit easier because using column-reverse flips the visual order of the flex items and also how scrolling works in relation to new items being added. Things like the "start" point of the scroll container are now at the bottom so newly added messages are kept in place. Without it we need to do the same thing but with some javascript.

Which is neat, but also causes issues with things like copy pasting parts of chat. So, it needs to go and replaced with some javascript intervention for scroll positioning.