feat: Allow Button to display an icon without a label

[dlnr]

Describe the pull request

While the story wants the tertiary button to be able to replace the IconButton component I've tied the Figma button API to the code. Because narrowing the "icon only" variant to just the tertiary button would require it be a separate component or have dodgy conditionals. Also the map wil need a secondary icon only variant or a button group of icon buttons might need a call to action.

What

I've reverted the changes to the IconPosition enum (not using iconStart and iconEnd) because using code connect this will match the React code snippet ,it saves a couple of properties and prevents the ability to have two icons in a button. It does introduce more variants in Figma, but this should be fine.

The label property was also not needed and the "icon only" variant introduces a span around the children with a visually hidden class.

Why

Previously an icon would have to be manually added to the children of the button, the size of button would be up to the developer, as well as adding a square attribute. There were plenty of ways to introduce errors in the rendering of the button. This fixes that while also having an API to change the position of the icon.

How

This PR introduces two props (icon and iconPosition) and conditionals to render the children.

Checklist

Before submitting your pull request, please ensure you have done the following. Check each checkmark if you have done so or if it wasn't necessary:

• Add or update unit tests
• Add or update documentation
• Add or update stories
• Add or update exports in index.* files
• Start the PR title with a Conventional Commit prefix, as explained here.

Additional notes

• This PR is tied to the linked Figma component
• After merge a code connect file will be uploaded to display the correct code snippet

[VincentSmedinga]

I’ve added descriptions to the examples.