Add icon position arg to buttons

[josefinalliende]

Issue

In PR #394, there was a case where the icon prop was used for text, and the label prop received an icon. This feels unintuitive to me. It was done solely to match the design’s icon/label positioning.

Example of current usage if WnFilledButton:

icon: const Text('Search Chat'),
label: SvgPicture.asset(AssetsPaths.icSearch, ...)

Proposal

It might be helpful to add support for icon positioning in the button components that support icons, so props can be used as intended (i.e., icon for icons, label for labels) without having to swap them based on layout needs.