Allow input textboxes to be resized

[cellio]

Request from here: https://software.codidact.com/posts/285911

When editing an answer, a user would like to be able to make the text area wider, taking priority over the right column if anything's there. For math or code the extra width can make editing easier.

It appears that we set resize: none in the CSS here:

co-design/src/common/_config.scss

Line 239 in b93ff7d

$textarea-resize: none !default;

. I don't know what the negative effects would be of removing that. I think, based on https://developer.mozilla.org/en-US/docs/Web/CSS/resize, that both is what would be needed to allow the user to resize. I don't know if we have to set that explicitly or if that's the default. (I note that my browser doesn't offer me resizing on this GitHub textbox.)

I don't see any harm in allowing users to choose to make post textboxes wider when they're editing, but I am pretty green with CSS. I'm also guessing that no change is needed in qpixel other than picking up an updated co-design; a grep for textarea-resize in qpixel turned up nothing, so I don't think it's being set there.