Make `MultiLineTextInput` Always Fit Its Content

[mad-moo]

As it stands, multi line text inputs are awkward to use. By default they are (vertically) small, only fitting in very little text. This requires scrolling in any but the shortest texts.

A common solution to this is to assign a larger height on the Python side, but this results in awkwardly large inputs, and still requires scrolling once the text becomes too long.

It would be nice for them to always resize to fit the text, maybe up to a given max-size.