feat(stack): add Stack component

[metonym]

Related #1384

Adds the Stack component.

Stack is a utility component that can be used to create a stack of elements with a consistent gap between them. It supports both vertical and horizontal orientations.

It uses layout tokens from the Carbon Design System to define the gap between elements. The default gap is 1, which is equivalent to 0.125rem (2px).

The gap scale can be set from 1 to 13.

<Stack gap={2}>
  <p>Item 1</p>
  <p>Item 2</p>
  <p>Item 3</p>
</Stack>