Make buttons with only icons square: Button

## Component/pattern to amend

When using a button that only has an icon inside of it, we should be able to have the same types of button that we have regularly, but with only icons inside of it, and it should be shaped as a square. Currently the button looks like a vertical rectangle when there is only an icon inside.

It would maybe also make sense to get rid of the small version, which is 27px vs the dense one which is 28px.

## Context

These buttons are often used as actions on pages, tables, or anywhere where there is no space for a full button. They always require a tooltip, as meaning can't be conveyed only through icons.

Locate the Button component or pattern and its existing size variants, then compare how icon-only buttons are styled against regular buttons. Confirm the intended square dimensions, including whether the 27px small variant remains, and verify that the requested button types consistently produce square icon-only buttons.

Written by the indexing model from the issue text.