feat!: Use new Button features for SearchField

[VincentSmedinga]

Describe the pull request

Comments in Search Field suggested reusing Icon Button. Now that we’re replacing that with an icon-only button, I wondered if that could be a drop-in replacement. And… it is! I found no visual or other regressions.

What

Use Icon Button for Search Field Button.

Why

Reuse existing components.

How

• Replaced the custom HTML button with Icon Button and remove associated styles and tokens.
• Decided to keep SearchField.Button as a better API than letting consumers use IconButton explicitly in SearchField.
• Decided to disallow the icon, iconPosition and variant props on Search Field Button, although having a visible ‘Zoeken’ label doesn’t seem bad either.

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

• Should we refactor SearchField.Input to SearchInput and make this thing a pattern?

[dlnr]

Seems like a logical change, which can also be done in Figma. But i don't get the extra layer of SearchField.Button.

[RubenSibon]

LGTM, but do address @dlnr's comment about using the Button component directly.