New "mini" size option for Icon Buttons

[pawelgrimm]

🚀 Feature request

Motivation

We have a precedent in Todoist of using icon buttons that are a little smaller than the "small" button size provided by Reactist

We should accommodate this with a new "mini" or "xsmall" size variant for the Button component.

Example

The context menu button and assignee icon on this task card:

Possible implementations

This new Button size should:

• Not add any margins or padding around the Button's children
• Accommodate icons of a 24x24 size